...but here's a new one that you may not have heard of: Figment, a social networking site for young adult writers! And I don't just mean it's for writers of young adult novels (although there is a strong forum for discusson there), but rather it's a site for writers who are young adults!
Figment was co-founded by Dana Goodyear, a staff writer at The New Yorker, and Jacob Lewis, the former Managing Editor at The New Yorker and Condé Nast Portfolio, so you know it's got good folks behind it.
So, hey kids - have your voice heard. . .er, I mean, have your voice read; join Figment and write on!