Social media sites have flourished and withered on a regular basis (witness Myspace, for which News Corporation paid $580 million in 2005, and then sold in 2011 for $35 million). The younger crowd gets bored easily and have a herd mentality. They will follow the crowd to the next hot thing. You can already see this by the Facebook demographics. The average age of members is getting older by the day. The advertisers see this as well, and it’s only a matter of time before they move on as well.