Teenage birthday parties are quite different than a young kid birthday party. While your teenager may be content to just call friends, their parents will probably appreciate a written invitation with your phone number and address along with an idea of when the party ends. As well, if party crashing is an issue in your town, consider noting that they must bring the invitation to get into the party. That will discourage uninvited guests from trying to intrude.
While your teenager may not want you to be a part of the party like you were when they were younger, make sure your child understands the rules and limitations and is willing to communicate and enforce those rules with their friends. You can help this by pointing out that if they do not handle this task, you will have to be there and that really won't be as much fun!
Most teenagers don't really want organized activities but are content to listen to music, watch movies, and talk. Make sure you are there to greet each guest as they arrive so they (and their parents) understand you will be there to supervise. Check in periodically throughout the party by offering snacks and such and stay unobtrusively within earshot.
