NEW YORK ( TheStreet)-- Zynga, the privately-held social gaming company, has reached a higher valuation than video game publisher Electronic Arts ( ERTS), according to SharesPost, an exchange for shares of privately held companies. Zynga, the San Francisco-based creator of the popular FarmVille and Mafia Wars titles, is worth about $5.5 billion while Electronic Arts is valued at around $5.2 billion. Zynga uses social networks like Facebook to distribute its games. The company has grown at lightspeed, increasing its headcount from 150 to 1,100 employees within the past 18 months. More than 215 monthly active users play Zynga games, according to the company. In comparison, Crowdstar, Facebook's second-largest game developer behind Zynga, has around 55 million users. Zynga generates revenue from the sale of virtual goods -- digital items that gamers buy with real cash such as a cow or corn FarmVille. While most virtual goods cost from $1 to $3, these figures can add up -- the virtual goods market is expected to reach $1.6 billion this year in the U.S. alone, according to Inside Network. Electronic Arts, however, has faced challenges transitioning away from a traditional brick-and-mortar business towards digital distribution. While the video game publisher begun to break into digital this summer through its acquisitions of social gaming companies Playfish and Chillingo, EA's shares have declined almost 4% in the last three months. Last quarter, Electronic Arts' revenue fell to $539 million excluding items, compared to $816 million in the year-ago period. The company has laid off more than 1,500 workers in the last few months. SharesPost bases its valuations on research estimates, trades of recent shares and funding round valuations. Shares of Electronic Arts were up 1.28% to $15.82 in mid afternoon trading. --Written by Olivia Oran in New York. >To follow the writer on Twitter, go to http://twitter.com/ozoran. >To submit a news tip, send an email to: firstname.lastname@example.org.