You should also enable Comment IP Logging for your journal (http://www.insanejournal.com/support/faqbrowse.bml?faqid=114). IP addresses aren't always helpful, but you'll need to have the user's IP address if you want to report the harassment to the user's Internet Service Provider.
Because there is no way to tie anonymous comments to InsaneJournal usernames, the Abuse team will not act in cases of anonymous comment harassment. If you believe that you know who is harassing you, or would like to take action against whomever is harassing you, you will need to follow the steps given in http://www.insanejournal.com/support/faqbrowse.bml?faqid=114 to track and report the anonymous user to his or her Internet provider.
When making a report, you will need to let the Internet Service Provider know that comments on InsaneJournal are timestamped in Pacific Standard Time (GMT -8) or Pacific Daylight Savings Time if the journal user is using the S1 style system, and in GMT if the user is using the S2 style system.