Pepsi Canada and Doritos Canada (both clients) get a lot of love in the April 1 issue of Strategy Magazine for the success of their social media efforts and their ability to connect and sustain involvement with their fickle youth audiences.  It's work that has won numerous awards and of which Proximity, BBDO and Pepsico are very proud.  (And before you ask, I'm not at liberty to disclose the effect on sales, though it is tracked.)

While the particular campaigns that cited in the article happened before I joined Proximity, I still got to pontificate about social media strategy as you'll see in the excerpt below from the article in Strategy's Youth Report by Emily Wexler:

When strategy and DECODE sat down with a group of teens, we asked if they were aware of various brands’ engagement in social media, and there was only one that the entire panel knew about: Doritos. For the past three years, the Frito Lay brand has been building buzz and experimenting in the social media space through its user-generated campaigns, “Guru,” “Viralocity” and the latest, “The End.” 
While the first two iterations asked fans to create videos, the latest campaign only asked for a 200-word write-up of how they would end a commercial – a much easier ask, resulting in entries that far surpassed their goal of 6,000 even in the first week. They also brought back a prizing aspect from Guru – 1% of future sales of the product – and are inviting the winner to be part of a “Think Tank,” providing their thoughts and opinions to the brand. 
The changes reflect a few lessons Doritos has learned along the way – that not everyone is a “creator” ready to make and post a video (more passive users need love too) and that making them part of the process can be mutually beneficial. 
“We truly want to democratize marketing this year,” said Haneen Khalil, marketing manager for Doritos, when “The End” launched.  
 “It’s easy to get fans,” says David Jones, VP social strategy at BBDO/Proximity Canada, Pepsi/Frito Lay’s AOR. “You can buy a lot of media and get a lot of eyeballs and attention, but they’re only going to stick around if it’s interesting and it’s used well and it becomes part of their life in a meaningful way.” 
That’s what Pepsi is attempting to do with the Pepsi Refresh Project (PRP), the ongoing global initiative steeped in social media, inviting consumers to submit causes they care about, gain votes and win funds for the project. After launching in Canada, Pepsi saw its Facebook fans grow by 100,000 in six months, says Neetu Godara, marketing manager, Pepsi Trademark. 
Last fall they ran PRP on campus, asking Canadian university students to take a picture with a sign describing what charity they care about and then spread the pictures via social media for a chance to win $5,000 for their charity and $5,000 towards their tuition. In six weeks, the number of fans increased by 20,000. 
Since its launch on Facebook in 2009, Pepsi has offered light-hearted engagement like the “joyous word of the day” to deeper interactions like backstage online access to MuchMusic’s MMVAs. 
As most brands present in this space have learned, Pepsi knows it has to keep the entertainment coming, and the dialogue open. 
“We not only respond to questions but proactively appreciate engagement on the page, so if someone posts a picture, we try to encourage it and validate that we’re listening,” says Godara, who notes that they have learned how to listen, and when to be part of the conversation – that it’s sometimes better to step away and let the fans talk among themselves, and that they’ll often come to the brand’s rescue. 
Godara also notes that brands shouldn’t be afraid of facilitating a dialogue with young fans, a sentiment echoed by BBDO/Proximity’s Jones: “Those negative comments are happening about you anyway. You can cover your ears and pretend they don’t exist [but] I would rather hear them and participate with the audience in some way to either make it better or at least pay attention to what is going on,” he says. “It may not be what I want to hear, but it’s pretty real and useful, and if brands listen, they’ll learn something about their consumers.” 

And if you've gotten through this shameless self promotion, I think you'd appreciate reading Ed Lee's excellent column in the same issue where he goes deeper on connecting with youth in this "post-social" era.