Facebook's 23-year-old CEO Mark Zuckerberg has hired Google Inc. veteran Sheryl Sandberg as the company's chief operating officer. Sandberg will report directly to Zuckerberg and will be charged with helping him grow the company. Sandberg worked at Google for six years and served as the company's vice president of global online sales and operations. The appointment follows a months-long search and comes at a time that the social-networking site is 'outgrowing its position as one of Silicon Valley's hottest startups.' Facebook's sales reached $150 million in 2007 but the company is not yet profitable and most of its business is in the United States. Zuckerberg has been quoted as saying the position of CEO was a challenge for him, and the young CEO faced criticism from users and privacy groups after Facebook launched a new advertising program. Some perceive Zuckerberg as arrogant, others as shy, though he has reached out to several older mentors in Silicon Valley. The growing company is now moving beyond Zuckerberg's core skills of technological savvy and product development and requires more traditional skills such as public relations and human resources management. Sandberg is one of many recent hires, including a new chief financial officer. The company is still searching for a general counsel. The previous COO departed after Zuckerberg refused to give up his role of CEO. A short history of the rise of Facebook and Zuckerberg's part in developing the company is given.