I looked through the Northern Ireland telephone book for the name Smyth, there are 10 listed but no Glenn A. Smyth. You could write all of them and see if you get information about him. He would be about 49 now? He may have had siblings born there.
It is the same phone book for the UK and I would look there perhaps he didn't like Ireland and so many people moved for economic reasons. Maybe he went back to England? You can easily look up Canadian, US and Australian, New Zealand phone books too.
Libraries often carry older telephone books so you maybe able to go back to one where he might be listed.