Zynga's CityVille arrives on Google+

CityVille, Zynga's hottest game on Facebook, is now on Google+.

Today Zynga announced CityVille's arrival on Google's new social-gaming platform. "Ultimately, we want to make our games accessible to everyone, everywhere--no matter where they play or what platform they play on."

This is really good news for Google. Getting into games in a big way with popular titles should help drive engagement on its fledgling social network. Launched as a "limited field test" in June, Google+ recently opened up publicly and has attracted 43.4 million members, AllThingsD is reporting. To really fly, though, Google+ needs to build the monstrous traffic and engagement that apps on Facebook have.

For example, Zynga's games on Facebook have more than 232 million active monthly users, while CityVille alone sees over 14 million daily active users. And just this month, Zynga Poker hit 50 million fans.

Of course, the Facebook platform combined with the viral nature of social sharing is the underlying force behind Zynga's success. The social gaming company is readying its IPO and is said to be valued between $15 billion and $20 billion. The San Francisco-based company took off in 2007 when Facebook opened up its platform to developers. Now five of Zynga's titles, including FarmVille and Texas HoldEm Poker, and are among the top apps on Facebook.

For every in-app purchase, Facebook takes a 30 percent cut. Google bets it can lure more blockbuster titles to its gaming portfolio by undercutting Facebook's pricing. Google is offering app developers a "promotional" revenue share: Google gets 5 percent from all in-app transactions and developers keep 95 percent.

Going forward, it's unclear whether Google will allow app developers to set up shop on the Google+ platform the way Facebook has. "We're slowly rolling games out," a spokesperson for Google+ told CNET. "We're still in a trial phase, listening to the developer community."

No matter how it plays out, Google and Zynga will likely remain close allies. The search giant is an investor in Zynga, and Zynga is an early partner of Google's new social-gaming platform. When it launched in August, Zynga Poker was among the first batch of game offerings. The addition of CityVille gives Google+ 19 titles, including Angry Birds, Global Warfare, and Dragon Age Legends.