SAN FRANCISCO CHRONICLE -- Zuckerberg, wearing his trademark hoodie and sneakers, defined Silicon Valley as “an idealistic place” that aims to “make an impact on the world” in his first public remarks on immigration, which were delivered to an ecstatic reception at the invitation-only forum. He appeared alongside his former Harvard roommate Joe Green, who co-founded the issue advocacy group Fwd.us. They co-sponsored the event with Define American, an immigrant rights group founded by Jose Antonio Vargas, a former San Francisco State student and Chronicle staff writer who made national headlines by revealing in a New York Times Magazine article two years ago that he is an undocumented immigrant. The evening was also the West Coast premiere of “Documented,” a film that Vargas wrote and directed. Vargas said he founded Define American to fight for citizenship for young undocumented immigrants brought to the United States as children, like himself.