Look at any advertisement for a fashion store, and you are likely to notice that most of the models are teens. In Western culture, especially, fashion is an extremely important component of teenage life. But "Why?" you may ask.
For teenagers, fashion is first and foremost a social statement. It is an outward means of expression to their peers and the rest of the world.
Fashion also provides teenagers a sense of identity by signaling which "grouping" they belong to ("prep," "punk," "goth," etc.). It may also signal a more independent or inclusive personality.
Teens can be extremely conscious about overall image when it comes to sexual attraction. They will often exploit fashion as a means to attract a certain type of person.
Rebellion may also be acted out via fashion. Since rebellion is often a huge aspect of a teenager's life, it is not shocking that teens often use licentious or shocking fashion to rebel against their parents, their classmates, and/or society.
Many teens pick up on fashion trends in an effort to stave off humiliation and mocking from peers. Poor fashion choices in the eyes of others can often be an open door to ridicule.
Often, fashion for teenagers is the result of the desire to be like a celebrity. Celebrities are perhaps the greatest influences on teenagers in the modern world, and they can have a huge impact on a teen's ideas about fashion and its importance.