Facebook employees at Menlo Park are seen on the Nasdaq board seconds before founder Mark Zuckerberg rings the Opening Bell for the Nasdaq stock market board 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.