Peer opinions take on new meaning in that their opinions are the only ones that matter. Evolutionary, this serves a tremendous purpose in preparing your teen for adulthood. And survival in the wild through reliance on peer supports. But in this day and age, survival means something very different. A clear social hierarchy emerges and kids intuitively know where they fit in with the crowd.
Many times, there is tremendous dissatisfaction with where they fit in and peer pressure can become very dangerous here. Teens may try to do anything in order to move up or down in the hierarchy. The pressure to conform to the norms can be hard to resist, especially if it means enjoying higher social status. The temptation to engage in risky behaviors is tremendous during this stage, not only because of peer pressure, but because risky behaviors act on the pleasure feedback loop making the positive sensations feel much more pleasurable.