I dont know why so many people want to know this, but because ARK is a Steam Game, it’s pretty easy to get the information how many people are currently playing the game.
You can just visit the page “SteamCharts”: Link
Currently (June, 9th) there are ~65.000 Players playing the game. But this number alone is not really meaningful, if you don’t compare it to other games. So let us compare ARK with Team Fortress 2: Link.
There are currently 67.000 Players playing team fortress 2. The interesting point is the all time peak. The peak of people playing TF2 was 117.000 Players. ARKs playerbase is rising every day. So it’s pretty likely, that ARK will get more players than TF2 – albeit being in ALPHA (Early Access) and as a paid game (TF2 is Free 2 Play).
It looks like ARK is a huge success. Let’s hope it gets even better. 😉