Kirjner upgraded Facebook's stock to "Outperform" from "Market Perform," saying that mobile advertising will drive revenue growth. He wrote in a note to investors that Facebook will likely be able to increase the number of advertisements its users view each day, with little chance they will see the additional ads as a "material deterioration" of their Facebook experience.
That said, Kirjner still thinks Facebook is a risky investment, because it depends on the long-term success of social advertising - a still new and unproven advertising model.
Facebook's stock is up $1.85, or 7.7 percent, at $25.85. It's still down 32 percent from its initial public offering price of $38.