Over the previous 16 years Free Pascal was downloaded 4.3 million times and Lazarus 5.7 million times from SourceForge
Which doesnt tell anything about the amount of people behind it, because the same person would over time download each version.
But looking at just the latest version 1.6.0 + 3.0.0, and just one OS (Windows)
over 53.000 win 32 Lazarus+fpc downloads on sourceforge
over 81.000 win 64 Lazarus+fpc downloads on sourceforge (may have duplicates with the above)
and another 72.000 Fpc only downloads on sourceforge (may have duplicates with the above)
Add to that downloads from mirrors, 3rd party [1] and svn.
For linux there are about 20.000 downloads (only counting lazarus), but then most linux distros have Lazarus in there repository and people may be using those.
[1]
getlazarus, codetyphon, download providers like heise.de/download, ...
I havent compared individual releases right now, but from memory I think numbers are growing.