Leaving strict instructions that its "not to be driven" is a bit silly....
Did you expect that your car would sit exactly in the place where you parked it, and not be moved until you picked it up?
If that was the case, they wouldn't have needed the keys.
86 k's however does sound like it's been taken for a bit of a joy ride.
If you have personalised plates on it, go and check the "spotted" thread.
If you don't have personalised plates on it, then it would be hard to pinpoint the car.