Let them be brand ambassadors
According to a report from the Pew Internet & American Life Project, 33 percent of teens, or about 8 million individuals, actively create content online. Many of these teens identify themselves through corporate brands.
Flexible, malleable messaging allows the teen to mold the brand and spread the word. When the message is disseminated by the teen -- rather than the corporation -- it carries more creditability. Forums where teens can create and propagate content for a brand spread positive associations.
Carat Fusion developed an excellent example of participatory interaction for Adidas on MySpace.

Teens create advertisements and share their work within their peer group. Not only does this particular approach allow for brand interaction in a controlled environment, but it propagates the brand through social networks and provides user data for future targeted marketing campaigns.