For any teen birthday a good idea I have seen is a "Limousine Scavenger Hunt". You rent like 2 limo's and you divide your friends into 2 groups, give them both the same list and have them ride around in the limo, trying to find the items.  Have them ask for things at homes and or find them on the street or something, but they can't go to the store and buy it.  For like a "Sweet 16" have them find for example:  16 CANDLES!, 16 grocery receipts, 16 shoes, 16 hairbrushes, 16 magazines, so on. Other ideas would be to find a purple flower, a hat, and so on like normal.