ULPT How do I find someone on other social medias?

Hi guys. I chatted with another user here, and after a while, they turned out to be a huge dck. They said disgusting things to me about myself and their girlfriend, I think it would be against guidelines to go into more detail. So far I only have his reddit username (which I think is just a randomly generated one), his age, and the country he lives in. The other things I could find out based on his comments isn’t very relevant. How could I bait him into giving me more information about himself? Like other social media usernames, an email, a full name, anything that would hep me find him, and then his girlfriend.

Usually I’m pretty good at this stuff, I found a guy’s whole family tree on facebook by just his private tiktok page, but I’m kind of stuck rn