Your best bet is to use the ask the staff section in the link below. http://emptyclosets.com/forum/ask-staff/ Start a thread in the ask the staff section. Explain to the staff what is going on in the situation. Give links and examples of the alleged harassment. The staff will take it from there.
Should you see a post that doesn't gel with EC's CoC, then you can bring it to the staff's attention using the report button (the little red triangle with an exclamation mark on the bottom left hand side of any given post). Starting an ATS thread is an option, but it's more work for you, and not anymore efficient at getting the situation dealt with.