A woman shoots a video of the sign at the entrance to the Facebook main campus. AFP/Robyn Beck
The puzzle game, which involves moving sweets to make a line of three the same color, is being played by more than 9.7 million people every day on the social network, making it the most popular game in terms of active daily users.
The top position on the chart, compiled by AppData, is more often occupied by a game from Zynga, like Farmville 2, which Candy Crush Saga unseated.
Facebook's head of European gaming, Julien Codorniou, said Candy Crush Saga was typical of the games coming from Europe that can be played on smartphones as well as on Facebook.
"The European gaming developers are really taking over," he said on Thursday.
"If you look at the top 10 gaming companies on Facebook a year ago, you only had one company, which was Wooga in Germany. Today you have six out of the 10, so there's really something happening here."
The most popular games were not revolutionary, he said, but they were social by design and they were fun because you played with your friends.
Alex Dale, King.com's chief marketing officer, said the games appealed to people, more and more of them women, who were not able to spend hours learning how to play console games.
"They want something that is going to deliver a burst of fun during the day, maybe during their commute," he said.
The fact that the games could be started on an Android or Apple smartphone and picked up later on Facebook added to its appeal, he said.
Facebook's Codorniou said European operators, such as Angry Birds developer Rovio and Wooga as well as King.com, understood how to successfully develop games across platforms.
"The bigger you are on Facebook, the bigger you in mobile," he said. "Eighteen months ago King.com decided to embrace the Facebook platform and amazing things happened."
The group said it had now generated more than 5 billion monthly game plays across all platforms.
King.com, which has main offices in London and Stockholm, has been profitable for seven years, and it has not had an investment round since 2005, when it raised 34 million euros ($45 million) from venture capital firms Apax Partners and Index Ventures.