I'm not a teen anymore, but I have some ideas from a party I went to when I was 17 that I thought was the most fun a kid my age could (legally) have.
My suggestions are as follows:
1) Drawings for prizes. Like CDs or other things teenagers these days like. Raffle them off towards the end of the night, but keep the things on display so they get excited for the drawing.
2) A mini casino. You can buy decks of cards and poker chips rather cheap, like a dollar each, and have adults deal out games of poker and blackjack, etc, for chips that can go towards prizes at the end of the night.
3) Pop and snacks of all kinds. We had every kind of chip and salty snack you can buy, and every kind of pop, too. We also had tons of gummy type snacks, as well as cakes and cup cakes, too. We all were amazed, it was like going to 7-11 and eating everything there for free!
4) A band is nice, but a DJ is more fun. Kids can request and dance and goof off to the music, music they picked and that they like to dance to. We all got a kick out of the DJ, too. He would play whatever we wanted, and that was beyond great.
Have fun! Hope I was helpful!!!