When I have found vehicles like this ( mostly down at the rivers around here ) I just give the cops a call with the numbers and they have told me if it has been stolen etc - with a couple that weren't they contacted the owner and gave them my cell no. so it could be moved before someone set it alight. which makes a lot more work for them. One had been dumped (we towed it to the local wreckers) the other one the owner was trying to find a way to to recover it on a budget ( they didn't have 8k so couldn't use the BOP guys

) we met them out there and got them sorted.
Other wise as others have said NZ Post or carjam will give you the owners info
There is no mechanical problem so difficult that it cannot be solved by brute strength and ignorance.