The reg number is no use, they will have a new one on it by now with a V5 to match.
What you need is the chassis number and engine number along with any dents and scratches that would identify it.
You need to talk to the owner and ask for as much info as possible, then tell the world, that will make it more difficult to sell on.
If there was any body defects that can also make it difficult to break for spares.