People have recently been discussing WoW population in one of the big threads, and in general, this is an often discussed topic.
I want to post a new site which hasn't been around before, which is relevant to that:
https://www.wowrealmpopulation.com/
They use a combination of one of the traditional approaches = seeded armory scans (you first seed your database with names of characters / guilds on each server, then you do armory requests for these characters and guilds, this gets you the names of new characters and guilds, and then you just do this periodically and the scans keep the database up to date), as well as something new = auction house scans (which quickly gets you tons of names of characters and guilds as well, a clever thing to do, because it is very fast and picks up tons of activity).
They have been doing it for some time, I watched them for the last year or so, their numbers were at first sporadic, then started becoming stable and useful wrt various big server groups, then wrt regions, and 6 months or so ago they felt confident enough to start reporting totals per region. Their totals qualitatively matched all important tendencies reported / seen on other sites, so I think we can now count this new site in as reasonably accurate.
So, what they report (for totals, scroll down):
EU characters in database: 3 759 008 of which 1 390 493 is currently considered being active within 2 week period.
US characters in database: 2 983 430 of which 1 091 575 is currently considered being active within 2 week period.
The definition of "active" character is:
"Active character: a character that has performed any of the following activities within 14 days since it was last seen: gained levels, looted something notable (my remark: to appear in the API log, that log skips loot that it does not think is notable in order to be manageable), made a honorable kill, changed or transmogged gear or placed something in the Auction House."
So, according to the site, US + EU currently have 2.5 million *characters* active. Given that this includes alts and that the period for doing something notable is fairly big (two weeks) and that something notable includes utterly trivial things like placing something onto the AH (covers tons of max-levels) or gaining a level (covers all of leveling chars), the number of active players is perhaps something like 1/2 or 1/3 of that -- although this is where we can make big errors, it is unclear what the coefficient for translating character counts into player counts should roughly be.
This misses China. They have some tracking for Taiwan (and Korea), but that's different (and small comparably).
In any case, the usual roster of warcraftrealms + wowprogress + arenatrackers got a new member, and it's good.
Please note that I am not saying that the game is dying or whatever. To clarify, it's rather obvious that BFA is doing terribly, and it has been obvious before. But 8.2 - if they really try - can perhaps stabilize things. And if they really try in 8.2, then who knows what's next, maybe they'll continue trying. This post is there simply to inform others interested in population figures / stats of a relatively new site that wasn't on the horizon before.