Could my stolen Mac have been erased before I activated Find My Mac? My Mac was stolen on a train and I only noticed it shortly before arriving the final destination. The thief most likely left the train at one of the earlier stops.

I activated the Find My Mac feature when I finally got home after I went to the lost and found office at the train station. I also remotely locked my Mac and activated the Play Sound feature.

Since then, I keep getting the same message, that "the computer is not online". I am wondering if whoever took it was able to open it and erase the contents and operating system on it before I was able to activate the security features.

Would that disable the Find My Mac feature, or would it still be able to locate my computer? (It's a MacBook Pro.)
If you don't have configured a password to choose boot options the thief is able to delete all your content, without having your root password.
He can simply:


Do not connect your Mac in internet.
Turn on Mac pressing Cmd+S to enter in CLI mode.
Change your admin account password (I have intentionally omitted details on this step).
Logout.
Login using your account with his password.
Disable all services related to iCloud, so disable Find My Mac.


In this case you're unable to locate your Mac.