suzi, i haven't read any other responses but i just want to put down my thoughts as they are coming to me. as quickly as possible - my husband had an online "stalker" for several years, well she got tired of dealing with him and moved on to me - basically trying to threaten my relationship with him and make me feel insecure by insinuating there was something between them (i know fully well there wasn't, for several reasons). she would call at 2 am, email me, etc. really trying to get my goat. point is, she STILL emails me occasionally, sends friend requests...it never ended until i ignored it. literally. EVERY time i responded, she fed off it. it kind of sounds like this is a chatroom type situation - i could be wrong, but if it is, is there a way for you, and some other of the people involved, to ignore this person? is there a room monitor you can report them to? also, i would google it - maybe there is another option besides legal action. or maybe just letting that person think you are taking legal action would stop it. i don't know. other than these 'stalling' tactics, i think realistically your only option might be legal action. have you tried just plain old calling the police? i think a lot of cities have cyber-crime units nowdays...at least they might be able to tell you the options. just my random thoughts...i know how invading and personal these attacks can be. i hope you find your solution.
(okay i went back and read some other responses - definitely pray for them suzi - but stand up for yourself. and don't forget to document, document document!)