In his first public interview since the bungled Facebook (Nasdaq: FB) IPO in May, Facebook founder and CEO Mark Zuckerberg admitted the stock’s performance has been “disappointing,” but emphasized the growing importance of mobile as a harbinger of better times ahead. The stock closed at $19.43 on Tuesday, roughly half of its original $38-per-share price tag.

Appearing in a T-shirt, jeans, and sneakers, Zuckerberg spent much of his interview -- streamed live via the technology blog TechCrunch -- fawning over the opportunities in mobile. When asked about the possibility of a Facebook phone, though, the 28-year-old billionaire said releasing a mobile device was “clearly the wrong strategy for us.”

Still, Zuckerberg went so far as to call Facebook a “mobile company,” saying “all the code that’s being written is for mobile,” and adding, with a hint of braggadocio, “You know the founder’s letter -- the S-1? Yeah, I wrote that on my phone.”

Asked about whether rival Google’s (Nasdaq: GOOG) Google+ “(ticked) him off a little bit,” Zuckerberg equivocated, but did say that search was something Facebook was moving into. He mentioned Facebook does “a billion queries a day, and we’re basically not even trying,” though he admitted later in the interview he was being a bit facetious. “We have a team working on search,” he conceded.

All in all, Zuckerberg seemed very excited about Facebook’s ability to integrate with Apple’s (Nasdaq: AAPL) iOS and Google’s Android platforms, also expressing confidence in the photo-sharing company Instagram, which was acquired in a transaction OK’d by the FTC in August. “They just crossed 100 million registered users,” Zuckerberg said. “They’re killing it.”

The founder’s appearance seems to have calmed investors somewhat -- the stock rose more than 3% after hours. When asked about the stock’s plunge since May, Zuckerberg even encouraged those currently with the company to “stay and double down.”

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