Zynga and Kabam each added games to Google+ Games platform this morning in the form of CityVille+ and Global Warfare. As of press time, it appears the core gameplay is identical to what players find on Facebook.

Zynga’s CityVille is still the largest game in the developer’s portfolio at 72 million monthly active users and 13.2 million daily active users, according to our AppData traffic tracking service. The game launched late in 2010 in a global release strategy that yielded Zynga’s largest game launch on Facebook to date. CityVille has been in decline across MAU and DAU since early June — interestingly, right around the time Zynga launched Empires & Allies, which incorporates city-building game mechanics borrowed from CityVille. It might be a bit much to say that CityVille “lost” players to Empires & Allies, but we do observe a shallow dip in Empires & Allies traffic that coincides with the launch of Zynga’s newest live game, Adventure World that supports the idea of faithful Zynga users migrating to new games as they launch without remaining in the old games.

Global Warfare launched on Facebook at the beginning of the summer, right around the time Digital Chocolate was readying Army Attack to take on Empires & Allies. A hardcore-oriented strategy title, the game never saw nearly as much traffic as the two casual strategy titles. Global Warfare currently enjoys 1.1 million MAU and just over 94,000 DAU, and has been in decline across both since August, essentially since developer Kabam launched Edgeworld on both Facebook and Google+.

As we’ve said before, it’s not clear how much viral growth games can expect to see on the Google+ platform, given that games are confined to a single point of contact on the navigation bar. CityVille at least has name recognition going for it, however, though perhaps not as strongly as Rovio’s Angry Birds. As developers experiment with the newly-launched Google+ APIs, we’ll see if app-makers come up with any new ways to attract attention to the Games tab.

UPDATE: Google is advertising CityVille on its main search page. Previously, we’ve only seen this space used by Google to advertise internal products.