As a teen, it is something that can be very difficult to control.

That said, learning self-control is very important, not just in the sexual sense, but also in eating and drinking (in addition to smoking - which is also something that is allowed, but in "temperate" quantities).

Learning sexual control is prudent too - I feel our society is "over-sexed." Avoiding these situations could help reduce the instance of STI's/STD's and unplanned pregnancies. After-all, we are designed to procreate within the bounds of marriage.

The Church teaches what she does on this topic since masturbation is using one's genitalia for their own wicked means.
It can contribute to the whole "trade" of illicit imagery that is so rampant in our society today. Even secular scientists are beginning to research "Your Brain on Porn" and note that the effect is VERY similar to illicit drug use. The need for more outrageous fantasies and imagery more often also matches illicit drug use, and eventually abuse. The other issue, which I touched on, is it is using the genitalia for pleasure. Sex is made to be this way - and is made in this way so as to encourage us to procreate. Masturbation takes the procreation out of the equation, and turns what should be "a good thing" (the genetic code contained within the semen) into filth that needs to be "cleaned up" and "washed away."

Now, despite all this, lots of teens and adults do battle with this habit daily. One of the best things I heard was to focus on the means of attaining your goal, NOT the goal itself.
If you focus on "not masturbating" constantly, then thats already the first thought, the "obsession" in the cycle of addiction. The Devil WANTS us to despair over the fact this is a difficult-to-break habit.

Instead, if we take this one step at a time, and simply try to make our lives more holy through the Sacraments, Prayer and faith in God - then these baby-steps are easier for us than simply daunting ourselves with "I Will not Masturbate."

And if you fall - try to take it as a learning experience. What went wrong that resulted in this?
Once you understand, put the event behind you and try to improve in that area. Go to confession, and most importantly, get Spiritual Direction and a Regular confessor. They can suggest further means of battling this habit, they can assess your culpability, appropriate penances and so on. There are some tactics that can be applied to some cases - but this can only be done in specific cases and is not appropriate for some people (as it can subvert Church teaching).

As a closing point, Fasting & Abstinence, when done correctly, can do great things in kicking this habit. As does a daily recitation of the Rosary and/or the Divine Mercy chaplet.
Also remembering that "idle hands are the devils workshop" is important. Don't leave yourself alone and bored. Its VERY dangerous.