List the reasons for teenage loneliness. How to get out of this state?

A teenager is very often lonely during his development. The fact is that he has already moved away from close ties with his parents and must go to a new, closer, interpersonal level of communication with his peers. However, not all adolescents manage to fit into the team, the team mercilessly rejects some adolescents, which is why adolescents begin a period of loneliness. Both parents and peers can help him to get out of it, the main thing is not to ignore it.