One of my favorite things to do at night as a teen was hang out in the resort hot tub. One time, we managed to get 30 teens in a hot tub for 20 and when we got out, the water level fell by almost a foot.
Another fun thing for teens is to go to the AMC at DTD. It's a dinner theatre so that should keep them occupied for a few hours.
For larger groups of teens, send them on a scavenger hunt. Collect pictures of hard-to-find areas at the resorts and have the teens get someone to take their picture in that spot. The Disney transportation system makes this pretty cheap to do. Give them a time limit and some kind of prize if they find everywhere. I'm sure we DISers can find plenty of pictures to keep your teens occupied for several hours.
well if they can get to universal i think they have a teen nightclub. other than that it's mainly pools, chilling at DTD or in the parks. The scavenger hunt idea i think is golden though.