Zynga on Thursday launched a 3-D version of "CityVille," adding a new dimension as well as a mystery storyline in a sequel to the online social game.

"CityVille was a runaway hit that brought players a truly social and fun city building experience," said the sequel's director of design Mark Nelson.

"CityVille 2 immerses players in a storyline peppered with quirky and interesting characters, while also delivering a beautiful 3-D town where players can compete with or play with friends as they build their unique city."

The original CityVille launched two years ago and boasted 100 million monthly users at the peak of its popularity but the current number of players is less than a fifth of that figure.

Zynga went 3-D in a revamped version of "FarmVille" released in September and has attracted more than 64 million monthly players, according to application metrics tracker AppData.

CityVille 2 is available free at https://apps.facebook.com/cityville-two/ and was to debut "soon" at the Zynga.com online playground.

Players take on the role of a mayor out to revive a virtual city by guiding the creation of businesses, museums, homes, roads, parks and other essentials of urban life.

Online friends can help build one another's' cities, consulting in real time using a newly added online chat feature.

CityVille 2 calls on players to deal with simulated urban woes such as fires, traffic and crime. The game also challenges players to figure out who or what sparked an explosion at the city's mayoral estate.

CityVille 2 rolled out globally in 15 languages.

Zynga last week announced it will be "parting ways" with five percent of its approximately 3,300 full-time workers and dump 13 games, along with significantly cutting its investment in "The Ville" franchise.

The cost-cutting moves are intended to let the San Francisco-based company focus on more promising games and ramp up its network on the Web and on mobile devices.

Zynga rose to stardom by tailoring games for play by friends on Facebook and went on to create its own online playground at zynga.com.