Well I'm not honestly sure how many people , including off the forums . I was always curious too.
Yes there are 5 million downloads in play store. There's also quite a bit of downloads in Chinese DQ and App store and Amazon.
Around 8300+ users in forums alone. A lot of people in Facebook dq too and overall.
Still, I don't know any statistics behind how many people play for eg. The forum users is countable since there's a table showing users that joined and active users in about page . Also it tells you the number in users page who joined forums.