People seem to just like to privately message those they are interested in, at least the people I've talked to did even if I wouldn't call it "friends" per se , so you could either try that yourself or just let it happen naturally through posting.
Although I never touched it myself, there's the Make A Friend Megathread specifically for this sort of thing:
https://sanctioned-suicide.net/threads/make-a-friend-megathread.164418/
There's also a site chat feature, though the exact requirements are hidden, you should be able to access it pretty quickly as long as you use this site for a while. Just look out for bad actors, this is a relatively public forum after all.