Even more impressive is the fact that those numbers represent just a fraction of the overall audience, as App Data's figures do not include users on Android phones or those who don't tie the game to Facebook.
"Enabling people to play Words with Friends on every device they have wherever they are has been the key to its success," says Zynga COO John Schappert. "We want to get one billion people to play together,"
And while Zynga has been slow to capitalize on that audience, it's planning to rectify that quickly.
"Words With Friends is an ad model that monetizes at a lower-level then pay-based games," said CFO Dave Wehner in the company's earnings call last month. "We're working to introduce new monetization techniques into With Friends games like we did with 'Scramble With Friends'. Coins and power ups, we're seeing those games monetize at a higher rate."
Analysts call the game a key property in Zynga's portfolio — one that is spawning sister games, like "Scramble With Friends," which already boasts a Facebook player base of 4.1 million players (a number that has increased by 700,000 in less than a month) and 1.9 million daily average users, according to App Data.
While "Words With Friends" is very much a casual game, the people who created it came from the core videogame world. Paul and David Bettner, who used to be part of Microsoft's Ensemble Studio (makers of the "Age of Empires" franchise), developed the idea after they had launched a small studio called Newtoy. Other team members included developers of massively multiplayer online games.
Words With Friends was actually the second game in the "With Friends" lineup from the company — the forerunner was a chess game. As it growth trajectory became clear, though, Zynga bought the company in late 2010.
Since then, the game has become a pop culture icon. Players who met randomly via the game's matching system have gotten married — and Mayer is hardly the only celebrity obsessed with Words With Friends. Alec Baldwin was famously removed from an American Airlines flight in December for refusing to stop playing after flight attendants asked him to do so.
Baldwin's spokesman Matthew Hilzik said at the time that the actor was "so in love with 'Words with Friends' that he would risk getting thrown off a flight to play."
That passion can work against the game at times, however. Though the addition of cross-play functionality between Facebook and the iOS and Android versions is seen as a huge growth driver now, it wasn't something that players initially embraced.
"We had a very public outcry [when we added the Facebook friends button] because we changed people's interface," said Vijay Thakker, CTO and Toy Maker at Zynga, at this year's Game Developer Conference in San Francisco. "The original reaction was 'You made my friends list bigger! You destroyed my life!'"
User data showed people were clicking on the button, however, so the company simply redesigned the interface to calm the outcry.
One unexpected impact of the Facebook addition was the game became less of a conversation starter among strangers. Before they were able to easily play against Facebook friends, people who met at bars would share usernames and compete against each other.
"The amount of games people were playing was up, but the number of invites was going down," says Thakker. "The game changed in ways we didn't necessarily expect."
And while the majority of Words With Friends players opt to play, well, with friends, some 30 percent still choose to instead challenge and play a random opponent.