Well, kids love money. Try to find something in your house that you don't need like I found a 10 dollars I-tunes gift card lying behind the couch. I don't really need this so I used it in a contest.
Don't put advertisements as an award. Teenagers (well some) don't like making website so they won't have a site which isn't fair.
A free customized rank, perhaps free access to the one forum that they may never access again, go for what David said and get them customized into a ChatBam hat, t-shirt.
I agree that advertising probably won't go too well, as most Will probably be teens.
A possibility of a reward could possibly be having their video featured somewhere that is known for videos? (Maybe getting it big on Youtube or something?)
You could also, as Lawson said, special rank or something.
The idea of creating customize clothes is a good idea, if you have lots of money. Unless you can find a service that can do it for free or a low price.
Special rank wouldn't be that great of a reward.
Hidden forum would be okay, but what will the hidden forum be about? And please keep it to yourself.
Probably a good clean access to an arcade is a good reward. Teenagers love games you know. Try and buy gift cards and sell 'em. Well, I ran out of ideas.
