Some people recommended lightspeed surveys in another thread. I don't know if they pay people under the age of 18, but it's possible. It's just a bunch of surveys, but they're too long and don't pay enough for what the "prizes are" (example: $10 paypal, $10 amazon giftcard, etc), but it's better than nothing, but keep in mind you have to qualify for the surveys.
Pinecone research is a better option, they pay (in less than a year, I've probably made about $80 or more with a bunch of $5 checks) but again, not sure if they allow underage participants, plus they don't have referrals, you have to find the right time when they're looking for people.
There was a thread from last summer or so that was for underagers like yourself, but you'd have to look real hard for it. It was doing surveys and the like, but I couldn't tell you what site since I'm legal and had no reason to look through it in the first place.