Contact your local police department who will be able to explain to you the cyber stalking laws.
A client attorney relationship has not been established with this answer. This is not intended to be legal advise or as legal representation. I am a Delaware, Pennsylvania and New Jersey personal injury attorney . Be aware that every state has its own statute of limitations; and statutes & case laws that govern the handling of these matters. it is necessary to consult an attorney in your jurisdiction to discuss the details of a case.
You could possibly seek a restraining order. The papers are easy to fill out and available at local courthouses. Start at www.lasuperiorcourt.org - I think any other sort of lawsuit would/could be pretty costly...
There's little that law enforcement will do for you, but take the steps necessary. You may have to file a restraining order. Bear in mind that the Internet is like fantasy land in that many of the people on the Internet do not use their real identity so to believe that you know who's doing it may take longer than you believe. I wish you the best.
The response above is not intended as legal advice since it’s impracticable to provide thorough, accurate advice based upon the query without additional details. It is highly recommended that one should seek advice from a criminal defense attorney licensed in your jurisdiction by setting up a confidential meeting. Moreover, this response does not constitute the creation of an attorney-client relationship since this message is not a confidential communication because it was posted on a public website, thereby publicly disclosing the information, which is another reason to setup a confidential meeting with an attorney.