People tend to gravitate towards the popular zones.
For example East Commonlands tunnel is the main trade hub on p99.
I'd argue with DMN that on green you'll see a lot of low level players! Try typing /who all 1 10 to see players non-anon/role who are levels 1 to 10. Strike up a conversation and see if they're interested in grouping.
Don't give up! p99 can be tough but it's more rewarding the further you get!
Edit: also be sure to check out the
https://wiki.project1999.com