I'm not going to litter this post with facts and figures. We all know them, and if you don't, there's more research on teens and social media on the Internet than you'll know what to do with.
Here's what I think brands can utilize to reach teens on the digital world:
Before you shut me down, know that I'm not recommending you go throw QR codes all over everything. We know that smartphone adoption is still growing among teens, and that BlackBerrys are big with them. QR codes are one of the only options cross-device options that the majority of teens with cell phones could engage with. Teens basically use their phones for communication, gaming and videos. If your brand has that content, throw it on a QR code and find the right places to put those codes where your audience is likely to scan them and would want to engage with that content at that time.
Teens like to go to concerts and other events that draw large youth crowds and often have brands integrating into the experience. Socializing the on-the-ground experience and providing interactive experiences is a great way to get teens to broadcast a valuable experience they are having to their friends online. If you want to take it further, try to find a way to engage their friends online who aren't at the event.
Teens aren't very interested in engaging with brands unless they're providing them with value at the time of engagement. Knowing where teens are and finding ways to engage them in real-time is key to tapping in to that utilitarian mindset. Maybe they're checking in at the mall or tweeting about their visit to your store. Instant engagement could and should happen right then and there.
Couponing/Contests on Facebook
Teens aren't huge "Likers" on Facebook, especially when it comes to brands, but they are willing to "Like" you for something valuable to them. Throw a coupon or contest their way and you'll get some "Likes." Depending on the brand you may get some good engagement on your page. For marketers the Facebook information you can pull is at least worth the trouble to gather insights about your fans.
Lastly I'd like to remind you that you have to promote your social and digital offerings to teens through other media -- in-store materials, TV commercials, print ads. If your brand is doing something great, let teens know about it! They're not the biggest social sharers, so you can't count on Facebook and Twitter broadcasting to drive results.