When I was ~15 and this was ~2004, some friends and I ran a forum with a lot of users and did some bad things where we would track down repeat banned users and screw with them. (In our defense, they were screwing with us.)

We used everything, from browser fingerprinting (and EFF only made the world aware of it 6 years later), looking them up in databases, tracing every digital evidence they left, etc.

Every little thing counted. What I learned is that people leave a lot of traces and you can collect these traces to dox them. The way you write is even sometimes fairly identifiable.