When it comes to anxious thoughts, teens are just as overwhelmed as a lot of adults. Over-commitments, poor body image, negative self talk and bad diets are just a list what some of the potential causes may be.
Take a look at this blog from Dr. Amen from Amen Clinics. One of the #1 psychiatrists in the world when it comes to understanding the brain.
This is a must read for any parent that has a teen struggling with anxious thoughts.