Development of Pinterest began in December 2009. The site launched as a closed beta in March 2010 and then as an invitation-only open beta. By December 2011, Pinterest had become one of the top 10 largest social networks according to Hitwise data. The company grew from 20 employees to over 100 focused on engineering, design, marketing and community. Pinterest saw extremely rapid growth, hitting 10 million U.S. monthly users faster than any other standalone site and reaching 48 million global visits by December 2012, a large increase from 9 million the prior year.