For the past week, I have been harassed online by my ex girlfriend and her supposed "friends". I have since realized something about these "friends". Is there any (legal) way to see if my ex share the same IP address as the "friends"?
Well, my ex has been spreading all kind of lies about me, harassing my half sister as well, and trying her utmost best to try and get me banned from deviantART. I need the evidence as a defense for if her shenanigans cost me my account.
Yeah, I'd garner as much info as you can about them with the minimum amount of response. You can get IP's from all over the place and you can actually harvest them from Facebook messages too.
Harrassment online is no different to harassment anywhere else, period. Collect the emails or messages, so that you have evidence of the harrassment, and then report the matter to your local police. Don't delete the messages, and let the police have access to them.
Don't bother getting into a slanging match. Do it lawfully. The police are currently taking a hard line with online harrasment, as they should. The perpetrators are cowardly and need stopping.