Mark Zuckerberg spun the mobile hype at TechCrunch Disrupt conference, and stuck with his slogan: "We don't build services to make money, we make money to build services." And clearly shows that Facebook still hasn't matured into being a public company.
They don't make enough money to justify their valuation, and they need to grow up and focus on making more money. Whether visitors come to Facebook through the web or on mobile, the reality is they don't visit when buying stuff or to be the target of marketing. They go there to gossip with their friends and family, until Facebook comes to term with that, they will continue to be a dismally performing stock.