As children grow into adolescence, it's natural that their relationships change too. Young children usually have a relatively large number of friends, and their friendships are often quite fluid, changing often. They want to spend time together to play or have fun. A teen is more likely to have just a few close friends, but will want to build a much more intimate and intense relationship with them. Play is no longer the main reason for friendship; teens talk (or communicate online). They turn to friends, rather than to their family members, for support in times of difficulty, to discuss what to do in a dilemma, and to celebrate achievements.
Peer pressure becomes a real force in the adolescent years. As teens start to forge their own identity and break away from the dictates of their parents, they turn to their peers for acceptance: They want to look and act like their peers, building a sense of belonging. In some cases, the desire to fit in with others has a negative effect, as the teen is pressured into delinquency by their peers. In other cases, peer pressure can be positive, as teens encourage each other to conform to accepted norms, and to take part in positive experiences.
Adolescents' growing emotional maturity leads them to develop relationships of loyalty, with friends who stay together no matter what. They also start to have intimate relationships and begin to experiment sexually.
The Internet, especially social networks (such as Facebook or Myspace), and mobile communication devices allow teens a level of connectedness that was not possible for previous generations. On the one hand, friends can stay in touch at all times, which may increase intimacy. On the other hand, they are able to develop quasi-relationships with large numbers of peers, some of whom are physically distant, and who they have never met in real life.