Thanks all. I'll file a complaint locally on harassment grounds and let the government legal system follow it up. I'm sure they'll purge private data quickly enough.
Doubtful. This has been threatened before and no action was taken. Private forum not a govt. owned forum. Good luck though.
If he lives in Europe, something similar to this is actually somewhat possible due to 'right to be forgotten' (e.g. anti-freedom of speech) laws. I am not sure if the forum specifically would be covered, however search engines would be forced to purge information related to his specific identity in certain circumstances.
Highly doubtful but I would love to see it tried.