Good luck, can't even imagine what this would be like. You'd think the police, with all the ANPR cameras about the place would have an idea of his location, I assume things like bank records etc... and passport details have all been checked.
Does he speak any foreign languages, or shown any interest in a specific area? Any old haunts he may have gone back to?
I'm sure all of this has already been asked... either way best of luck.