Scratch

So it will not be made?

What
It wasnt even started to be made

I don't get why everyone here tries to start all these super-ambitious projects from the start, requiring knowledge they don't even have and no one else has either.

Start simple, and once you've mastered the simple, then and only then go on to the complicated. Make your own personal website from scratch, and refine it over time. Then, learn PHP and maybe make a simple login system or whatever. Then, refine your PHP skills and maybe try to build a simple CMS, and from there you'll maybe have gained almost enough knowledge to build a project as huge as this one.

Learning enough to do something on the scale of a social networking site will probably take years from my estimation (as someone who doesn't know much about web development, but knows that this is a horribly complicated subject). Especially if you want it to be up to par with other, similar sites for the same purpose (i.e. Facebook) and if you want W3C standards compliance.