Facebook founder Mark Zuckerberg is seen on a screen in Times Square moments after he rang the Opening Bell for the Nasdaq stock market board from Menlo Park on May 18, 2012 in New York, United States. The social network site is set to begin trading at roughly 11:00 a.m. ET and on Thursday priced 421 million shares at $38 each. Facebook, a Menlo Park, California based company, will have a valuation exceeding $100 billion.