Rose Michee Smith

Hello, my friend is being cyber bullied on a blogging site called Tumblr, this bully is speaking on anonymous so we cannot find out who it is. She can stop this happening by removing the ask box from her blog however they are threatening with things to prevent her from doing this. My friend is thinking of going to the police about it but is wondering if tey would be able to find out who it was and if they did how would they punish this person?