Why do you need to know?

If she is in the hands of LE, is there anything you can do to help?

If she is a friend who needs your help, why can't she work out how to contact you?

If you want to know what happened to her out of prurient interest then you should just back off.  She may have other reasons to lay low

IMO, that tells you everything you need to know whether she considers you a client that she's friendly with  
or a real life friend she intends to stay in touch with. That line is pretty clear.  She may just want to lay low. She might have simply moved on to better things. Or maybe she got busted.  

If you're just wanting to find out if she's been busted or not, no one is stopping you from searching public records.  However, best to just let her go if you ask me.

If a massage parlor was shut down it would have been in the local paper.

If you don't know her real name, her non hobby phone, have an email address for her, etc, She is not your friend, she is just someone you have become friendly with, not to be confused with a real friend.

If she wants to be found, she will be. In the meantime if you care at all for her, respect her wishes not to be found.

she resurfaced.  Outside if watching the local news, nothing you can or should do.