Is it worth someone posting this question on concertina.net? (If it hasn't already been done - but I took a quick look on there and couldn't see any threads about it.) I don't belong to that forum, and am not part of the concertina scene, but one of them might either have an up-to-date phone number, or live locally enough to go to his house, ring the bell, and push a note through his door if nobody answers.

If it were me, I would also ask some of the neighbours when they last saw him. And if that comes up zilch, I think it's time to alert the Gardai. Fingers crossed the scenario doesn't get that far.