Hi Yanes,
Welcome to the forum. Hopefully it will be working better soon.
I'd say over a 1000 are registered but most of those are not active users. People come and go. Sometimes they reappear months later. Some register and never post at all. You can never know how many are just viewing or whether they are actually registered.
There might be about 30-50 who are registered and who make ongoing posts, but that is a real guess.
Other members may tell you this is wildly inaccurate and they are probably correct.