I mentioned about building a site about off-line businesses or a local news portal before.
How about a site aimed at teens and where they like to hang out?
Review entertainment spots, cafeterias, music stores etc. Also, have a chat room/forum.
Focus on getting the local teen community to frequent the site, then introduce Ads paid for by local businesses and maybe have point cards/vouchers that are exclusive to the site.
The points could be accrued by activity on the site since that helps generate views on the Ads.
Edit: and for the forum, maybe have it invite only to keep out adults masquerading as teens.