There's more than one correct answer...
1 - Probably some of the same exact demographic that originally found it and grew up with it to now.
Teens in the 2000's.
Specifically.
Teens in the 2000's, still living, eating, drinking, breathing the same "I don't give a fuck about what you think" attitude from the 90's that got killed by 9/11.
That's the demographic in my own opinion/theory but the flames that burned within said demographic has long since been quelled, soooooooo...
2 - The real demographic these days is, technically, again, the result of said 2000's teens.
Stale men in their mid-20's to late 30's, no longer familiar with the 90's attitude that used to flow through them and this site thanks to political correct-ness, now coming back to relish in what the younger generation's been drawn to --- Friday Night Funkin'.
Not that there's anything wrong with FNF, just that there's certain kinds of people that maybe should be focused on other things in their lives, or at least something a little more hardcore and true to the roots of this site.
But otherwise, Friday Night Funkin' has definitely attracted the wrong crowd; some even let their small children play the game.
And that's fine since they're going to add a full "No Naughtiness" mode later on, but still.
3 - Gen Alpha (4-13 y/os).
As I said, Friday Night Funkin' has attracted the actual demographic it set out to not attract, thanks to its look and sound, and especially thanks to those damn content farms on YouTube Kids; the ones we all can agree to openly despise together.
Anyways......
Goodnight.