Zynga’s CastleVille social game, the newest title in a series that has entertained more than 100 million Facebook players, is off to a fast start since its launch six days ago. The game is the latest title aimed at making sure Zynga’s initial public offering, expected after Thanksgiving, stays on track.

Last night, according to internal data from Zynga, CastleVille crossed five million daily active users. By comparison, CityVille, the most successful Zynga game to date, only crossed 3.2 million daily active users six days after its launch, according to AppData.

AppData hasn’t yet updated its numbers on CastleVille and still shows the game at 2.7 million daily active users. But there’s no doubt that the game is growing fast.

As we’ve noted before, CastleVille joins other recent Zynga games, including Empires & Allies, Adventure World, Pioneer Trail (formerly FrontierVille), Words With Friends on Facebook, and Mafia Wars 2. The title mashes up Zynga’s usual cartoon style, which has a wide appeal among Facebook users, with more interesting game play than it has had in the past.

The game was developed by the Zynga Dallas team the company acquired when it purchased Bonfire Studios last year. Bill Jackson, creative director on CastleVille, told us the game has next-generation social features, in a recent interview. Those include faster social interactions and a focus on a player’s reputation for helping others.

In the game, you build your own kingdom. It’s like a combination of Pioneer Trail and CityVille, except in a medieval fantasy setting. Zynga launched the title today in another 17 languages. As such, the game is going to be tough competition for Electronic Arts’ The Sims Social, which has 6.1 million daily active users.

In the global view, CastleVille is clearly a move to hold on to the No. 1 position. About 68 percent of CastleVille players are playing at least twice a day. Zynga says that in six days, 135,176,035 quests have been completed. Players have expanded into new parts of the map (covered by dark Gloom spaces) a total of 4,594,750 times. About 23,845,983 beasties hae been banished. Some 8,262,768 baby cows have been raised. And 182,360 Bubbly Grogs have been crafted. I haven’t gotten around to the latter task yet.