Now it's time to decide what kind of party your teen wants to have. Costumes or no costumes? Decorations or no decorations? Theme or no theme? Teens most likely have firm opinions on all of these items, so it's best to get on board with your teen's vision, as long as it's in the realm of appropriate.
Teens are less receptive to formal activities than kids are, so if you want to encourage planned activities, you're going to have to come up with something pretty cool. One activity that may lure even the most apathetic teen into play mode is a whodunit murder mystery game. You can buy a boxed game or make up your own using instructions from the Internet, and guests can come dressed as their favorite Clue characters.
Since most teens are into music, perhaps a music-themed party would appeal to them. They could come dressed as their favorite rock stars, and you can set up Rock Band in front of a big screen or use a makeshift stage with a karaoke set. But don't be disappointed if they want to dial it down and just have dancing or a scary movie, sans the costumes. Remember, they are teenagers.