I'm thinking I should have posted this before, but later is better than never :). I saw this article on about.com and I think every teen should read this, whether or not they're making money online or not.

http://parentingteens.about.com/od/moneymanagement/a/teen_income_tax.htm

But, from what I've gathered from reading for  about an hour on taxes, it all depends on a couple things. However, I'll apply it to readers of this blog (my target audience - 13-16). Dependent, Single (not married), and not making an income that has been tax- reduced (as in, taxes have been taken out, thus, less money). However, if you are making over a certain amount  (the exception was $400 for single self-employers) then you will probably have to file for taxes. As well, if you pay checks are tax-deducted, then you will need to file in order to be refunded (unearned income).

Hopes it helps :).