The fastest-moving game developer on Facebook recently has been Digital Chocolate, which has raced ahead of other mid-sized developers over the past month with a gain of over seven million new monthly active users.

The company is rapidly becoming one of Facebook’s biggest platform companies; with 24 million MAU and four million daily active users, it is poised to overtake Playdom, whose traffic has slowed since its acquisition by Disney.

Throughout its growth on Facebook, Digital Chocolate has been eager to define itself as a different sort of company, and it’s certainly not slacking off on that message now. “There are a lot of interesting companies out there, but a lot are actually products, not companies,” president Mark Metis told us yesterday. “The ones that are companies were built in a different era, when virality was easier and lightweight apps could slide.”

Digital Chocolate’s growth is coming in part from a rapid-fire series of releases, four of which are skins of platforms already in use by other games. One might assume that Digital Chocolate is pushing all the new users in via advertising, but Metis said that isn’t the case.

13 Apps By Digital Chocolate (New Games Bolded)

“Far and away our biggest source of user acquisition is virality,” Metis said. “We’ve also built significant cross-promotional scale, and that has enabled us to get exposure to our games very quickly. And then we feel like we’re bringing unique and new offerings to the market. Advertising is far and away our lowest source of user acquisition.”

Whether Digital Chocolate can power its way into the upper echelons of Facebook developers may depend on games it hasn’t yet released. The six newest titles are just the start. “We haven’t used all of our bullets, I can tell you, and you’ll be seeing some additional interesting games in coming months,” said Metis.

Digital Chocolate’s success so far may give pause to those who haven’t taken it seriously in the past, when it released several games that didn’t pan out. It’s those failed games, along with similar failures in mobile gaming, that will make Digital Chocolate stand out over all of its competitors in the future, according to Metis.

The plan is to cross-develop titles for both Facebook and smartphones. That has already been done for MMA Pro Fighter and Millionaire City, which Metis says have done well on the iPhone. Future titles will be carefully designed to provide good experiences and interoperability across both the web and mobile.

That plan isn’t unique; Zynga, CrowdStar and others have either talked about or made moves to do the same thing. Metis thinks the idea will start to get real traction next year. “I think 2011 will be an interesting year for social gaming on mobile, and we’ll start to see some significant levels of success. It won’t reach its peak, but serious traction will be gained,” he said.

Even with all its plans, Digital Chocolate is trying to stay disciplined and grow at a measured pace. “This isn’t a rollup, and we’re not trying to pile employees on quickly,” says Metis.

For more on Digital Chocolate’s plans, also check out our lengthy interview with CEO Trip Hawkins from August, done before the company hit its big growth spike.