Editor's note: Amy Henry is vice president, youth insights, of C&R Research, Chicago.

For all the curiosity surrounding the number of Baby Boomers flocking to Facebook, social networking is still a young person's game. Membership among teens age 13 (technically Facebook's age limit) to 17 grew an impressive 90 percent from 2009 to 2010, with 257,000 joining in June 2010. This shouldn't come as any surprise. Both Facebook and its closest competitor, MySpace, are ideal to meet the needs of older tweens and teens as they become increasingly focused on learning the complex rules of friendship, and especially how friendship plays out in today's world of online connections and virtual relationships. But marketers, beware. Courting the under-18 crowd using traditional tactics has always been tricky. Those intending to campaign on this turf for their hearts and minds must step carefully and stay true to the unwritten ground rules of authenticity and relevance. A brand's success with youth via social media channels hinges on establishing a presence that delivers a sense of community that tweens and teens can then use to tell the rest of the world that they "belong" to the brand as much as the brand belongs to them.

It helps to first understand where the 13-to-17-year-old crowd stands developmentally. While they understand that the friends they keep say something about who they are, they may be less aware that it's perfectly normal for youth in this group to  "try on" different types of friends. But this behavior plays a powerful role in teens' search for identity. By associating themselves with different kinds of friends, they not only get to see what it feels like to play different roles within a group, but they also get to see how it feels to assume different personas. Wondering where they fit and to whom they belong makes social status and standing a borderline obsession for most tweens and teens. Social networ...