Bad Idea.

Trigger Warning: Mentions of hate crimes and discrimination against autistic people. Includes murder. Also, lots of "but the family!" stuff.

There was a post to my page, on Facebook. It was marked automatically as spam and I deleted it, so I doubt you saw it, or who it was by or where it linked to. And it was at least a week ago by the time you see this. I could have rearranged my queue to fix that, but... I'm about to rip the post to shreds in many ways, and I suspect the page owner would prefer you not know who they are. (If they show up here and tell me they want the shreds-ripping linked to their page, I'll do it. But I doubt that's the kind of publicity they want.)

Dear Admin I invite you to visit my page I made for my 19 year old Autistic brother, could you please like it and share it with everyone, if you don't mind.

Dear Admin. I know this isn't personal, then. Probably stuck on as many pages as possible. Not a great sign, but eh. I did the same when trying to draw attention to Autistics, not Monsters. I didn't write "Dear Admin," though, and I gave each page a few moments glance to see which pitch would work best.
I made for my 19 year old Autistic brother. You capitalize Autistic, and it's identity first. That's a good sign. But you made it for? I am a bit worried, here. Because, you see, I know how often family members make this sort of page and then share things about their autistic relations they really have no right to publicize, without the consent of the person they post "for." So I worry. 

I'd be grateful . The purpose of my page is to spread awareness about this disorder among common public too.

Awareness. I know that awareness ranges from great to horrible, and I don't trust it because the people doing good awareness tend to also be aiming for acceptance and nowadays often say "autism acceptance." But there are enough who don't know. So, I'm trying not to be too hard.
And I know there are many who still know nothing, or close to it. I disclosed to one, about eight months ago. It was the smoothest disability disclosure I've ever had, and by far the best- he had only my word to take for what being autistic means for me, and no insistence that he knew my disability better than I. (People who have gotten good awareness are fine; people who have gotten bad awareness are far harder to disclose to or talk to than those who know nothing.)

People with Autism are as much a part of this world as we are.

Um. This seems kind of othering. And "we." Um. Hi. I'm Autistic. This is one of my super-huge pet peeves. You do not speak to me like I am a neurotypical family member, you do not write to me like I am a part of some "we" that is different from autistic people. You now get no benefit of any doubts going forward. None. Because you just assumed that the person you wrote to was allistic, and you probably don't even know you did it. You probably never thought of the possibility that an autistic person would read this, but you should have.

About 1 in 88 children has been identified with an autism spectrum disorder (ASD).

OH GOD YOU WENT THERE. No. Stop. Stop right there. Children? I know children is the age group where we've got 1 in 88 diagnosis, but we've got a British study finding 1% autistic spectrum in adults living in households. Not institutions, not group homes, plain old households. So that means that at least 1% of adults are autistic too, stop talking about freaking children like it's just kids who are autistic you are part of the reason people think we're all kids when we're not. You are adding to this problem. And people will ask where the autistic adults are and even with your brother an adult (19>18, he's an adult even if someone decided on guardianship and he's never allowed to use that fact) you probably won't know where we all are because you don't see us and you don't think of the idea that we are here.

The high prevalence of autism is of major public concern, especially for families like mine who are already affected.

 I mean, it is, but not for the reasons I suspect you're going to go for. Especially when you're going "families like mine who are already affected." Know what we need? Civil freaking rights. Medical freaking rights. For people to stop deciding our lives are not worth living. For people to stop giving sympathy to our murderers. For people to quit trying to neglect us to death. For them to stop succeeding. Those things need to be of major public concern. So does education- real education. That doesn't need to mean intensive academics for us any more than it needs to for anyone else, but that same academic rigor needs to be an option if we decide we want it, and not a "you'll have to fight for it and make a national level fuss for it" option. A "here, it's right on the list of paths we're suggesting" option, with accommodations as needed. Just like vocational schools should be, for everyone.
I mean, yes, things like respite care (called babysitting when the kid's not disabled...) are important. Maybe, just maybe, if people weren't fearmongerers with their awareness campaigns, there would be more babysitters willing to learn to work with autistic kids? More extended family members willing to watch their autistic relations?

It's stressful for them and stressful for parents to come to terms with seeing their child change from "normal" to a withdrawn silent stranger who adopt unusual behaviours throwing tantrums, in frustration and depression at not understanding the bewildering world around them.

Ok. So you use the ou, not just the o. Which means you might actually be in Britain. Maybe not, but it's at least possible. If so, that study was in your country, in your newspapers. CHILDREN?! CHILDREN?!
And the whole change from "normal" thing. That's not how it works. Neurotypical kids don't suddenly become autistic. And conflation of meltdown with tantrum is not OK. I was a small child once. I threw tantrums. Not often, but I did. I also had meltdowns. I still have meltdowns and shutdowns both. I have no clue how you would mistake either my meltdown or my shutdown for a tantrum, but apparently people can't be bothered to learn the difference. Either that or they think pushing and pushing and pushing a person in meltdown until they do push back in order to toughen them up or something is smart.

With patience and love we must try to get at least a glimpse of what their world is like.

Or, you could, I don't know, read the things we write! I can't with this. I just can't. With the patience to sit down and read a freaking blog post or book or to sit down and listen to what your autistic relative is telling you, even if spoken language isn't (maybe never is) how they tell you. I can't always talk. Amy Sequenzia never talked. Evie talked a little bit, when she was younger, but she stopped (possibly because seizures, I don't know.) Henry Frost doesn't talk. There's a lot of us who don't talk, or who talked late, who are still saying things, and your autistic relative can tell you things too.
I mean, yes, there is some patience involved in understanding what we want and need, but that doesn't actually require understanding what our lives are really like. I hope "glimpse of their world" isn't a final goal, and the implication that our world is not your world (same world, we just perceive it differently) is kind of creepy. 

The disorder varies from mild to so severe that a person may be almost unable to communicate and need round-the-clock care.

There's a lot more variation than that. It's not a strictly less disabled to strictly more disabled continuum, and it's not a strictly less autistic to strictly more autistic continuum, and even when you can get a general sense that one person is more "obviously" autistic than another that doesn't correspond with generally more disabled, and there's situational differences too. That's before we get into "my child is lower-functioning autistic because of all these conditions that aren't autism." Functioning levels really don't work well. Amanda Baggs wrote about that, a bit, and how dangerous it can be when a person thinks they are strictly more disabled in every way. I imagine family members who think their relative is strictly more disabled in every way are just as dangerous.

I would also like to mention that a large percentage of Autistic children live at home and are supported by their families.

CHILDREN. Want to know the percentage of children in the general population who live at home and are supported by their families? It's pretty big. It is, in fact, considered the normal way for children to live. Shocker.

There are several challenges and hardships faced by such families.

Ok. There are. And you do need more. You're asking in the wrong place. I don't know if you've ever seen the diagram of who you vent at and who you comfort? Disabled person can vent about their disability issues (ableism generally to blame for most of them) to pretty much any close relation. Close relations vent to further relations, friends. And outward it goes. You are a relative of a disabled person. I am Disabled, same disability even. You do not vent to me. You vent elsewhere. You get your resources from further outside the circle, or you take what is offered freely.

Showbiz is a very powerful media and unfortunately used mostly to exploit Autism and to make more market value.

I'd like to know what they are doing to exploit autism and autistic people, according to this person, but my guess is that they're upset about autistic characters on TV because "stop romanticizing autism" (on their page) doesn't sound much like "Autism Speaks, stop fearmongering for money!" to me. It sounds like "You're portraying autistic people as real people with lives but also as the butt of jokes! Stoppit!" Which, um, no. We need to be in stories, we need to see people like us. Do it better, yes, please, but keep us in your stories. The accidental autistic characters shouldn't be better characters than most of the purposefully autistic characters (Dan Harmon's Abed may be an exception. Michael's Clay definitely is.) 

Families with Autistic members are in need of social support and awareness and the fastest way is through media.

That's true enough. But what autistic people need and what you want? Somehow I doubt they are the same.

Please support my page and cause to utilize showbiz to prevail awareness about Autism.

Basically what I said last sentence. I don't think you know what actual autistic people need. More of the same awareness most organizations try to spread isn't it. More family members talking about how hard it is to be related to us isn't it. More people complaining about autistic characters being actual characters isn't it,