Actually, this is not a "new" trend (thanks, TV news, for making a story where there isn't one). Cutting has been going on for quite some time. Speaking from experience.
I knew young girls doing this, around 1990, maybe it bears some relationship to the needle thing we used to do when I was growing up. You catch the first few layers of skin, and stick the needle through so it hangs on you but no blood, blood is just an added dimension,
Also speaking from experience...went to high school over 20 years ago...this is nothing new. A good book on the subject is called "The Bright Red Scream" by Marilee Strong. Still struggle with this every now and then, but as an adult I understand what brings me to want to do something that most would find repulsive...