"Simply put: we don't build services to make money; we make money to build better services," Zuckerberg wrote in his letter to prospective shareholders. "And we think this is a good way to build something. These days I think more and more people want to use services from companies that believe in something beyond simply maximizing profits."
People who've observed Zuckerberg closely say his age is an asset. His is the generation that grew up with social networking, with computers all around them and the Internet as something that's always existed. Many of his employees are younger than him, as are a lot of the up-and-coming technology entrepreneurs with whom he competes.
"I don't think you could build a company like this if you were an old guy like me," says David Kirkpatrick, a 59-year-old author who chronicled the company's early history in "The Facebook Effect."
Kirkpatrick, who is also founder of Techonomy, a media company that hosts conferences on the relationship between technology and economy and social progress, first met Zuckerberg six years ago. He says he was impressed with his vision, even then.
"It's the willingness to take risks, the willingness to abide by a very contemporary vision ... I don't think that he's too young. I think most CEOs are too old."
Zuckerberg, who lives in Palo Alto, Calif. with his girlfriend and a white Hungarian Puli dog named Beast, has matured as a leader with the help of experienced mentors.
One of his closest advisers is Sheryl Sandberg, whom he hired away from Google in 2008. Zuckerberg, known for sometimes-awkward public appearances, realized that the razor-sharp, people-savvy advertising executive complements his own shortcomings. Sandberg is Zuckerberg's No. 2, the chief operating officer who oversees advertising and often serves as Facebook's smiling, public face.
Then there's Donald Graham, the 66-year-old CEO and chairman of The Washington Post Co., who serves as a mentor to Zuckerberg and holds a seat on Facebook's board of directors.