
Facebook’s C.E.O. Mark Zuckerberg rings the Nasdaq’s opening bell from Facebook’s headquarters in Menlo Park, Calif., on May 18, 2012, the day of the company’s initial public offering, while Sheryl Sandberg, Facebook’s C.O.O., looks on.

Facebook’s C.E.O. Mark Zuckerberg rings the Nasdaq’s opening bell from Facebook’s headquarters in Menlo Park, Calif., on May 18, 2012, the day of the company’s initial public offering, while Sheryl Sandberg, Facebook’s C.O.O., looks on.