I have several tips for teen parties!
Everyone will bring their own alcohol anyway, but if you want to provide some, get loads of packs of These little weak French lagers or similar from your local supermarket. And also as someone else said, cans of soft drink and individual water bottles will be drunk far more readily than buying 2litre bottles of anything.
Provide a big bin or your wheely bin and a big sign on it saying, "BOTTLES & CANS IN HERE" or they WILL end up in your flower beds. Also a large bucket of sand for fag ends.
If you are providing a bin full of beer in water/ice, get some of the same 0% alcohol ones as well to mix in with them. When the labels come off, just scoop them out of the iced water and the kids will drink the 0% ones as well quite happily without realising. Do this before they arrive, leaving some of the normal strength labels still on the bottles or floating in the water.
Do provide lots of snacks, even of they seem quite "Childrens Birthday Party". Mini Pepperamis, Mini Baybels, Wotsits, Dip and Crudites, those mini chicken skewers, cheese straws, a bowl of Celebrations etc on big trays get eaten really quickly, even by the most sophisticated of teens. Don't bother with plates/napkins as they won't get used.
If you're allowed to be around, a big Pizza delivery ordered by you at about 10.30pm goes down well and sobers kids up very quickly. Or pizzas in the oven, done by you.
We've had parties quite successfully here, the only thing that gets problematic with my boys is the loudness of the music which needs to be kept to a certain level due to neighbours. They also don't invite the (mainly girls) known to down a bottle of vodka quickly and end up crying and sick.