There are lots of reasons teens self harm:
Essentially teens self harm as a coping mechanism. They can do this to distract their thoughts from these other feelings or urges. Below are some things that teens might be self harming to cope from:
-Depression
-Eating Disorders
-Peer pressure
-Trama
-Abuse
-Bullying
-Low self esteem
-Feeling out of control (self harm may let them feel in control of something)
-Strong feelings (anger, grief, loneliness)
-Addiction
There are plenty of more examples of things teens need to cope from by self harming. There are also different reasons to self harm (ie. There is a "rush" from self harming that becomes addictive; asking for help in an indirect way; some do it because they want to get rid of apathy. Apathy means feeling numb/nothing; punish self) , but, again, a major reason is to "distract"/cope from other issues in their life
Hope this helped!
~Just a girl in love with Shawn Mendes