http://bodybuilding.about.com/od/bodybuildingfaq/f/TeenSupplements.htm

The response posted on this page is IMHO pretty much dead on. He recommends a good multivitamin, EFA's, and a good protein powder and that's it. Realistically no one "needs" more than that regardless of their age, but certainly when you're still a teenager you've got testosterone out the wazoo (which is a technical term), and therefore already have an advantage over us older folks.