Harassment is a term used more for the workplace, but you have been wronged. A private wrong is called a tort. Seek out an attorney in or near where you live, Explain how your ex came to have the pictures (it goes to permission). It may be that the attorney suggests a letter asking to have the pictures taken down (cease and desist), with the letters both to the ex and the web sites.
We do not have a client/attorney relationship until you make an appointment, we discuss your case face to face, I accept a retainer, and we explictly agree to enter into representation.
Often times this type of scenario can be taken care of by the local police department where the individual who is violating your privacy lives. Call their non-emergency telephone line, describe the situation to an officer, and request that the officer contacts the individual and politely asks him or her to stop.
Should this not work, you may need to consult with a local attorney, who could send a strongly-worded demand letter to the individual threatening them with legal action should they continue to violate your privacy.
Disclaimer: This does not constitute legal advice. No attorney-client relationship has been formed through this answer.
This is a common concern on this board. Essentially, you have two potential legal claims against the poster - violation of your right of privacy (if the images were taken without your knowledge or consent), and violation of your right of publicity (if the images were published without your consent). Since nudity is prohibited on FB and Twitter, you should be able to report the images to the abuse department of these sites, and get them taken down. If you own the copyright to the images (i.e., you created them) then you can send a DMCA Notice to these websites, and demand that the images be removed based on violation of your copyrights. You may also have the ability to press criminal charges against the poster, under Florida's computer abuse statutes, depending on how the images were obtained by your ex.
Disclaimer: The foregoing does not constitute legal advice or form an attorney/client relationship. Please contact an attorney for formal legal advice on any specific matter.