It is possible to "work" with people knowing only a nickname. If I can do that, enemy can do that too.
That's fairly simple, when you read someone's messages online, you can concentrate enough to feel the person and to work with that person in astral plane.
Also I've noticed, that if I ask for help and mention any specific problem, they gonna target exactly that.
So before asking for help, make sure your question hasn't been answered already.
Once when I posted an idea how to use necronomicon with RTR, after a couple of days I had a very strong spiritual attack. I was fine, but two people (friends of friends and friends of family) + animal at family house died at the very same day. And I had a warning that my life is in danger before that.