Pretty Simple's Criminal Case is a hidden object game on Facebook. It has also just recently surpassed 100 million users, an impressive figure for any social game, and currently sits at about 6 million daily active users. "It's difficult to reach this size on any platform," Pretty Simple's head of communication, Serge Versille, tells Gamasutra. "Reaching just a million players is something that even big developers have problems achieving and when the game came out we had only 35 people." Pretty Simple is keeping revenue figures under wraps, only stating that Criminal Case has garnered total revenue in the "eight-figure" range. Presently 50 members strong, the Paris, France-based studio is now looking to bring Criminal Case's success to mobile through the iOS store in early 2014. To do that, Pretty Simple first isolated just what makes the game so attractive to Facebook's userbase. "This sort of crime scene investigation gameplay didn't really exist on Facebook before Criminal Case came out," says Versille. "Doing something new, obviously, is going to get us a foot in the door and some early interest. But building on that, we really needed to do things right in terms of virality and retention." The model for Criminal Case's gameplay is conventional of free-to-play titles on the Facebook platform: Users get a certain amount of daily actions and can obtain more via friends or microtransactions. Where the game distinguishes itself from its contemporaries is perhaps the rich text and tone of its police procedural format -- which, together with weekly updates, turns it into an interactive version of the sort of ripped-from-the-headlines crime dramas that millions of television viewers enjoy. "Obviously that same audience is on Facebook," says Versille. "We just tapped into it." Moreover, Versille says, the view of the Facebook market looks quite different from Europe. While reports circulate concerning the flagging performance social giant Zynga (Farmville), companies in Western and Northern Europe including King (Candy Crush Saga) and Pretty Simple see an enormous platform with high guaranteed visibility simply not afforded by the currently impacted mobile market. "It's the best distribution platform for free-to-play games right now," Versille maintains, a view also held by company co-founder Bastien Cazenave. "In our opinion, the opportunity is unparalleled today. Even in light of something like Steam... We're talking to a billion people on Facebook, whereas on Steam you are looking at 65 million. And that's a different audience as well." Now setting its sights on mobile, Pretty Simple hopes to leverage its existing 6 million daily active users in a new market. "King does this very well, progressing from platform to platform," Versille notes. "We definitely want to offer them a different experience that makes sense on mobile." Pretty Simple expects that being a known quantity will help Criminal Case stand out from the pack -- far more than a fortuitous windfall like an App Store feature and plentiful press coverage. "Obviously we want to pull out all the stops and make the mobile version everything that it should be. But that goes along with creating a relationship with Apple and making a game that is as compelling to our Facebook players as well as a new mobile audience," says Versille. "Retention and virality are the two pillars of the success of any game, social or otherwise. One part of it is common sense: people see what their friends are playing and want to join in. The other part is more esoteric, creating the right social feedback loops -- that 'virtuous circle' of play." The studio is set to launch on iOS within the next few months. Building the team, Versille says, has been the hardest part. "Everyone wants mobile developers these days," he laments. "It's difficult to find good people you want to work with and who can build their own app. I don't mean to diminish the rest of the project's challenges -- the user experience, bugtesting, and so forth -- but recruitment has definitely been the key thing for us, from my perspective." Further reading: -Mike Rose: Are social games on Facebook really dying out? -Serge Versille: Criminal Case: our path to 4M DAUs