Four days after opening CityVille on Facebook, Zynga is calling the new game its biggest-ever launch. Some 290,000 people played the title in its first 24 hours, according to the Zynga, with 25 percent continuing long enough to set up a franchise in a friend’s city, an action that takes at least 15 minutes of game play.

CityVille’s first-day performance is only important in context, though. Zynga had two other major releases this year: Treasure Isle and FrontierVille, in April and June respectively. Both games had slower starts than CityVille, followed by rapid growth:

It does look like CityVille’s growth will continue to surpass FrontierVille, from this early vantage point. However, note the hockey-stick growth that Treasure Isle enjoyed beginning on its sixth day in the wild; it’s unlikely that CityVille will be able to surpass those gains, which left Treasure Isle at its peak of 27 million monthly active users after just one month.

Treasure Isle can’t necessarily be repeated, since Facebook made some of its biggest viral channel changes the same month that game was launched. As for CityVille, Zynga tells TechCrunch that its growth is primarily organic, not from advertising.

The list of techniques Zynga used to create CityVille’s early growth spurt would likely be quite long, but as we noted on its first day out, it includes email campaigns and inciting new players to invite their friends over from FarmVille. There are also social mechanics like staffing your government buildings with friends, which helps push out invites and interaction between players. Our preview lists more, including an in-game economy that creates money and goods from connections.

Zynga’s cross-promotional abilities can’t be rivaled by any competitor — it’s simply too large in comparison to others — but given CityVille’s growth so far, the title will likely serve as a template for the next round of new social games.

The historical data on the chart above comes from AppData Pro, which also offers additional metrics.