There is very little you can do, because you don't want to do it.
If you want this to stop, don't post on those sites.
Don't reveal any personal data.
Whatever you do, don't ever meet anyone you've become acquainted with on the Internet.
There are creatures on the 'net far more threatening than trolls.
If you stop, he, it, she, they will be stopped.
You refuse to stop, he, she, it, them won't ever stop, either.
If your fears were credible, the site moderators would act.
They won't.
You should.
Be careful.