Behold, explorers! We have stumbled upon the world of supplemental vitamins! Maybe you took a multivitamin as a child (perhaps, those awesome Flintstone ones?); you might still take one today. Even with a daily multi, food is still important. That's because a multivitamin/mineral supplement can't supply the required amount of all the different nutrients teen bodies need.
However, if you know your eating habits are less than optimal (you prefer candy bars to glasses of milk? Don't we all...) vitamins are a good supplement when your body needs those extra nutrients. So if you don't want to ditch your pizza for spinach, might be a good idea to take some multi-vitamins. To be sure, though, check with your doctor to see what your specific needs are.