Zynga could be filing for its long-rumored initial public offering as early as this week or next week, AllThingsD reports. The article cites unnamed sources “close to the situation” as saying the company’s filing will reveal more “robust” valuation numbers than previously reported for the company’s speculated annual revenues.

A Zynga IPO this month would come as no surprise given both the company’s history of rapid growth and successful game launches on the Facebook platform (and long-standing speculation about an IPO). A recent filing shows that the FarmVille developer appears to be selling $490 million in Series C Preferred shares that had been slated to take place in early March, which would corroborate earlier reports that Zynga was raising $500 million in funding with a $10 billion valuation. AllThingsD reports that the valuation may be much higher when Zynga files with the Securities and Exchange Commission, citing the $9 billion valuation LinkedIn got at market despite having half that in valuation pre-IPO.

According to our social game traffic tracking service, AppData, Zynga currently enjoys 247 million monthly active users and 49 million users across all its Facebook apps and games. Its largest game, CityVille, accounts for over 30% of that traffic. An ISG tipster tells us that Zynga is about to launch a beta of its newest game on Facebook and that the title of the game may or may not be called Crime Nation.