Couple of points
its your blog,son enable ip logging on the ***rd
if the person does not have a static ip address, a geo location search will lead you to the internet service provider
Any non public information obtained can't and won't be used in a court of law.
S***estion:
Grabb the IP adresses of those people,look them up and ban their ip,also use cloudfare,it will block/recognize vpn's