Find a way to contact the owner of the site and bait them with something like an acquisition offer, you might be able to use the email in the whois data if ther

Find a way to contact the owner of the site and bait them with something like an acquisition offer, you might be able to use the email in the whois data if there is one. The point is to get the owner to click a link you provide, behind this link you want to log IP/Headers, maybe do some JS fingerprinting/etc... It is unlikely they will open this link over VPN/Tor. If you feel like it check your server logs to see if they have accessed your site from that IP and when. Then send a C&D containing all this information and tell them that you have legally contacted their ISP for their subscriber information and not only will they be sued for violating DMCA for possessing your data but that they will also get hit with the CFAA for circumventing protections against access and that they will enjoy a five year sentence in a federal pound me in the ass prison.