It's pretty much impossible to find out how many users still are out there. You'll have to find every Amiga forum worldwide and ask how many people have how much Amigas. There are lots of country-specific forums which have unique users - i.e. users that use only that forum.
Take Germany for example - the Amiga is still relatively huge there but only a limited number of those users visit international forums. And then there's the French, Greek, Italian, Spanish, Dutch and other forums which are spread out across the world.
And then there are lots of people who use Amigas and who don't visit Amiga forums, or read those forums but do not participate in them.
I say: for everyone who would reply on such an international survey there's another 1, 2 or maybe even 3 Amiga users that will not respond. Basically, it's like trying to count how many fish are swimming in the Atlantic. You *might* have an idea, but it's still a very, very rough guess.
Therefore, my guess is that there are some 15,000 people in the world who more or less frequently use an Amiga (even for only a game), and have an average of 1,7 Amigas. Then there are still another 34,500 Amigas stored in people's attics/basements/cupboards.
Result: 60,000 Amigas worldwide that are still alive.
And finally: 73% of all statistics are made up on the spot :-)