It's nonsense. I knew many kids in highschool who did various forms of cutting, and the one common trait they shared was not that they were all going through any kind of serious problems (they weren't, it was all common boyfriend/girlfriend stuff). What they shared was the inability to stop showing off their cut marks to each other constantly, almost as if they were some sort of trophies or achievements.

The reason teenagers cut themselves is twofold. One, because they're surrounded by other teenagers who are all trying to "out-adult" each other other, and two because they are surrounded by adults who trivialize their problems and make them feel like anything they're going through isn't important or serious.

Cutting helps with both of these issues. When you cut yourself, you attribute the actions as a response to some problem that you think you have. The act of self-harm helps solidify in your mind the idea that these things you're going through really are serious and important. It helps you feel like an adult, and gives you the impression that your life is more dramatic than that of your peers. This is the reason that all the people who do cut themselves somehow can't stop letting everyone around them know about it. That's the point.

Try getting a sharp razor and cutting some part of your skin. You'll quickly notice that it doesn't actually hurt that much (or at all really). But the blood, wound, and scar that result are dramatic. It gives you tastes of that "adulthood" that all adolescents crave, makes you feel deeper than your peers, makes you feel like you're a warrior wounded in the battle of your life circumstance that nobody understands. It's incredibly low-cost and high-reward. It isn't difficult to understand how it can get addictive.