Facebook’s shares are trading at $40 Friday afternoon.  They debuted at $38 following an early high of $42 on the Nasdaq exchange.

These numbers from the initial public offering mean that the site’s 28-year-old founder, Mark Zuckerberg, has, according to Forbes, become the world’s 23rd richest person and many other employees instant millionaires.   The company itself made $16 billion.

Founded in 2004, Facebook can boast 13% of the world’s population as its members.  This figure, comprising more than 900 million people, has grown year on year and its current $104 billion valuation puts it ahead of both Disney and McDonald’s.

Unfavorable comparisons to Google, which has double the valuation but ten times the revenues, has many skeptics warning against investment.  While previous priorities centered around creating new ways for people to communicate online, Facebook must now prioritize gratifying investors and Wall Street.

Facebook has already acknowledged the importance of mobile devices in its quest to increase profits going forwards.  The relative lack of real estate on a smartphone screen makes presents obvious advertising problems, and earlier this week General Motors withdrew its paid ads from the site.

Supporters point to the company’s history of success and the popularity of social games as one potential key to maximizing mobile profits.

While going public is a gamble that hasn’t always paid off for online companies, Facebook’s sheer size and relative youth mean that it certainly could prove to be worth more than $104 billion.  However, at this point the consensus is that $38-$40 per share represents a dicey investment until more is understood about the Facebook’s inner workings.

If the company can figure out a way to clamber over The Great Firewall of China and add another 500 million users then many of these doubts will disappear – but a strategy for achieving that makes solving the mobile revenue conundrum look like an appealing headache.