PALO ALTO, Calif. — President Barack Obama likely has a few more "friends" after a town hall at Facebook headquarters Wednesday, but the real winner may be the medium of social networking itself, which commands not just the attention of politicians but now an appearance from the president.

At the same time, the openness and accessibility praised by Obama himself as a key value of social media clashed with the tightly controlled nature of the event.

Questions came from pre-screened online submissions or hand-picked Facebook employees, and ranged in topic from the national debt and immigration to education and health care.

To anyone who tuned in via a live online feed, it wasn't very different from its televised counterparts. The only difference might have been the average age of the fresh-faced audience, many of whom appeared to be the same age as event moderator and Facebook founder Mark Zuckerberg, 26.

Zuckerberg offered the first question, asking the president about his plan to curb the federal deficit.

Afterward, employees were quickly shuttled out as they rebuffed reporters' attempts to interview them. Facebook is known for its rigorous effort to control its media image, and Zuckerberg seldom grants interviews.

An employee offering a glowing review of his employer and Obama's visit was interrupted by a company spokesman, who declined to give media access to audience members.

It was a stark contrast to Obama's easygoing introduction, when he introduced himself with a joke about the famously informal Zuckerberg.

"My name is Barack Obama, and I'm the guy who got Mark to wear a jacket and tie," he said.

At the end, Zuckerberg presented Obama with a hooded Facebook sweatshirt, the CEO's signature attire.

The event was held in a vast warehouse space on Facebook's Palo Alto campus, just down the road from technology industry stalwarts like Hewlett-Packard Co. Before Obama took the stage, the room buzzed with the anticipation as before a rock concert as employees, industry luminaries, politicians and celebrities such as M.C. Hammer gathered for the Silicon Valley social event of the season.

House Minority Leader Nancy Pelosi, D-San Francisco, posed for smartphone pictures with young admirers, while Jeremy Stoppelman, co-founder of the consumer review site Yelp.com, shared thoughts on how he believed social media could help small businesses. Members of Congress and state government mingled with hundreds of potential voters.

Obama was the first sitting head of state to visit Facebook's brick-and-mortar home, the latest big-name visitor to the tech-savvy region in Northern California that gave rise to social media and the personal computer. He will likely not be the last: the 2012 presidential race is expected to see unprecedented use of social media as a tool to reach voters.

The event capped an influential year of milestones for Facebook, which reached 500 million users last July and became the subject of a critically acclaimed and Oscar-nominated movie. Zuckerberg famously built the site in his dorm room at Harvard just seven years ago as a service for classmates.

Today the privately held company is valued in the tens of billions of dollars, maintains offices around the world and has more than 2,000 employees. Zuckerberg, now a billionaire, will be 27 in May.