I know first hand of some pretty nasty incidences of blackmail and related games against models. Sometimes you can act on it, sometimes not. Getting some expert help to find and expose them is the ideal solution.
Most threats are pretty slight, mild, and manageable and in these instances call their bluff (ignore them) and do your thing to contain the problem. Cut off all communication, check your security, and close off any areas that you know they have accessed. Most times this will be enough to stop them, especially if they are phishing for information (a common ploy).
Serious threats you must treat pretty much the same, but be prepared for any eventuality. Exposure is fine compared to being under attack, and you may just get lucky or find the right support to find them first. The longer you can delay, make them doubt the accuracy of their information, the more time you will give yourself to make plans. Record every communication.
To end on the positive note, I know models (more than five) who still work today, years after someone published their identities including some that had addresses of their families exposed. One even had a whole web site dedicated to her '(her real name) camwhore' , she is still working and doing well today, her family not knowing what type of work she does yet.
