Sorry to say this coin has not been seen in my cache on the Hampstead Heath in London since September 2011. It's possible that muggles found the cache and have taken it, but more often lost TB's/Geocoins have been taken by some "Geocaching beginners" who don't know what it is or how to log it. Sometimes a look at the cache logs around that time can give more hints about its whereabouts, but often there's not much to do about it.
I'm going to marke it as "missing" (move it to unknown location) to stop it from showing up in the cache all the time, despite not being there.
That said, I had geocoins that disappeared and turned back up somewhere else 5 years later... probably also moved by some inexperienced cachers and never logged. So there's still some hope...