According to this post Tapas has over 50,000 creators so I imagine if you add readers to that (while also acknowledging overlap) it's quite a lot.
Now if you wanna get all fancy about specifics, counting active versus dead accounts, suspended accounts or duplicate accounts (multiple accounts run by the same individual but for different content types like original versus fanwork) then maybe the numbers could get a bit more fuzzy but it's still a sizeable amount of folks