What: Shares of mobile social game maker Zynga (NASDAQ:ZNGA) are getting clobbered today, down by 13% as of 11:53 a.m. ET, after the company reported fourth-quarter earnings and issued disappointing outlook.

So what: Revenue in the fourth quarter came in at $185.8 million, with bookings of $182.1 million. Adjusted net income was a mere $0.4 million, which rounds to $0.00 per share. Nearly all user metrics were also down, including average daily active users and average monthly active users, among others. Significantly, the number of paying players declined as well.

Now what: Zynga also announced that it was acquiring Zindagi Games, maker of the popular Match-3 games. Guidance for the first quarter was soft though, with revenue expected in the range of $160 million to $175 million. Bookings should be just $150 million to $165 million, and Zynga expects an adjusted net loss of $0.01 per share to breakeven.