If you really want to do teen, find a way to shoot your own. it converts better and has a much less generic feel. If you start out looking like every other teen site you will be competing against a thousands of others. Shoot your own and set yourself apart. It's less expensive and you have control.
However, if you need some good teen content and insist on buying it. Send me an icq and I will point you in a couple good directions.
There are a couple great content providers on this board for sure. Some that I have bought from for other projects. Hit me up and I will share.
http://www.1stcontent.com/
The link above has some of the best content on the board in my opinion.
Vic Lagina is also top notch! Do a search using that screen name and you will find his site.