The most notable and popular is The Gay Youth Corner - there are many gay, bisexual and possibly straight people on the forums. (See relevant links.)
glooork.com
Texting websites for teens are websites where teens can text to and from their phones for free.
There are many great websites for teens on the Internet. Try searching 'awesome web sites for teens'
www.teen.com
Tumblr
Hook4minors.wall.fm
Yes
I can think of one famous bisexual off of the top of my head: Lady Gaga.
9gag or funnyjunk are quite good websites to go to for teens who want a good laugh
coolmath-games.com and disney.com
imvu.comhabbohotel.comourworld.comevony.comhope they help!
yes! its slapface.spruz.com
Spin the bottle is a good dating site for teens of all orientations.