Don't get caught up in the training routine's that the pros put out in the magazines, those will only lead to overtraining. Remember these guys are on steroids and have all day just to lift, eat, and rest. They don't have to go through 7 plus hours of school and all that other junk we have to do.
The routines they do are good for them, but may not be good for you. You have heard many times before, no two people are created equal, and this applies to bodybuilding also. So when it comes to training go back to the basic compound exercises and keep it simple.
It is very important to not neglect any muscle, especially your larger muscles, like legs and back. Those are two commonly neglected muscles, and the two muscles that if you get them big everything else will follow. You should base your routine around the compound exercises, these are exercises that involve multiple muscles to help move the weights.
Main Compound Exercises
Those are the more basic exercises for each muscle which you should be able to do the most weight for also. I would recommend sticking to these exercises listed above or a variation of them. Don't get too caught up in many cable and machine exercises.
Free weights are more superior in terms of gaining mass. Machines are more for isolation and you really don't need those unless you are training to enter a contest or your physique is at the point to where you are satisfied or you are big enough to start worrying about "detailing" your physique.
I doubt many teens are at the point to where they need that. I know I am not even near that point. You should also be keeping your sets and reps relatively low.
If you don't have the proper nutrition to feed your depleted muscles after being torn down by lifting, then doing many sets will just tear them down more and more and if you don't have the proper nutrition they won't repair properly and you will only be tearing them down worse. You won't be gaining, you might be losing.
For your smaller body parts do about 6-8 sets, and for bigger body parts do about 9-12 sets. Keep your reps relatively low to gain some good size and strength, we are all looking to get bigger and stronger muscles. The so called "best" rep range is from about the 6-10 rep range, I think it is pretty true. Sometimes I will go for a heavy workout and train in the 4-6 rep range, but that is for variation.