Social gaming giant Zynga Inc. (ZNGA) swung to a second-quarter loss and cut its full-year forecast, disappointing the Street and prompting a massive sell-off in after-hours trading.

The “Words With Friends,” and “FarmVille” maker’s report was highly anticipated as a possible indicator of what we may hear from Facebook (FB) when it reports its first financial results as a publicly traded company on Thursday.

Zynga now expects full-year adjusted earnings between 4 cents and 9 cents a share, well below the Street’s forecast for full-year earnings of 27 cents a share.  The social media company cited, “delays in launching new games, a faster decline in existing web games due in part to a more challenging environment on the Facebook web platform, and reduced expectations for 'Draw Something.'” 

Draw Something is the game Zynga acquired through its purchase of mobile gaming company OMGPOP for $180 million. 

Zynga reported a net loss of $22.8 million, or 3 cents a share, compared with a year-ago profit of $1.4 million, breaking even on a diluted basis. When adjusted, the company reported earnings of a penny per share, compared to adjusted earnings of 5 cents a share one year ago. 

Revenue rose 19% to $332.5 million, up from $279.1 million in the second quarter of 2011.

The results were below the Street’s estimates; analyst consensus was for 5 cents a share on revenue of $344 million, according to Thomson Reuters.

Daily active users rose 23% compared to the year-ago quarter, to 72 million, as monthly active users increased 34% to 306 million. Zynga founder Mark Pincus, who’s chief executive for the company touted the launch of Facebook’s current number one arcade game “Bubble Safari,” and the launch of “The Ville.”  He also boasted of revenue growth in its advertising business of 170%, and a total of 300 million monthly active users, and 33 million mobile daily active users, making Zynga the largest mobile gaming network, but he noted the recent challenges the company has faced.

"We also faced new short-term challenges which led to a sequential decline in bookings,” Pincus said. “Despite this, we're optimistic about the long-term growth prospects on mobile where we have a window of opportunity to drive the same kind of social gaming revolution that we enabled on the web."

So far this year, shares of the gaming company are down 46%, with most of those losses occurring since May, after questions about the revenue model of social networking site Facebook arose after its initial public offering. Zynga’s user base is heavily tied to Facebook’s platform, and concern about slowing growth and user activity has put downward pressure on shares.

Shares of Zynga were up 3% in Wednesday’s session, closing at $5.08 a share, but the stock was down more than 40% in after-hours trading. Facebook shares slid 7.5% in reaction to the company’s results.