As far as health, to summarize a vast amount of information on what is said to be one the most researched supplement aside from steriods:
Creatine isn't known to cause any problems from research aside from reactions to it from loading phase (which isn't always necessary), which can include cramping and diahrea. Another thing would be your body holds more water so you must drink tons of water, most companies recommend a gallon.
Now aside from that there aren't any major problems known, the problem is that the supplement isn't all that old so there isn't necessarily a difinitve source for that info.
One thing that I've read both ways is that creatine affects the muscles and the heart is a muscle, I've read that it can help prevent heart disease(s), but at the same time it being a muscle and not knowing complete long term effects makes me curious.
I suggest you read this, probably the best report on creatine I have read.
Now aside from the health.
Is it necessary for teens to take creatine, I'm not so sure on that one.
Creatine is supposed to be great for breaking through plateaus and such.
That being said. Unless you have been training for a fair amount of time, the rate at which you can experience gains with the high level of testosterone in a teens body is exponential. Maybe a little protein to help, but you get my point.
Good luck, definately read that link if you want some well written info.
I'm still neutral on creatine (haven't used it myself) but I'm not a big fan of the number of guys that hear their buddy used it and so they run down to their gnc and buy a tub of it. Creatine is a supplement you do have to bust your butt in the first place to get the real gains of creatine. I know guys that take and don't work that hard in the gym, and really it doesn't look like they go to the gym at all, but then there's guys such as my coach who jumped his bench from 350 to 400 in a month.