John, from Bridgend, was last seen on Monday, June 17, 2019.
The now 78-year-old was on holiday with his partner in the village of Argassi, heading towards a monastery on Mount Skopos.
Despite searches by the Greek authorities, and later by a team from the Western Beacons Mountain Rescue, he has not been found.
His family have appealed for anyone who may have been in the area to think about whether they saw John, who was wearing a royal blue shirt.
They have also asked holidaymakers to scour their own photographs to check whether John was in the background of the shot.
The investigation is being led by authorities in Greece, but if you have any information which you think may help, you can contact us by one of the following means, quoting reference 1900243231:
- Live Chat https://www.south-wales.police.uk/
- Online https://bit.ly/SWPProvideInfo
- 101
Information can also be given via Crimestoppers anonymously on 0800 555 111, or their online form at: https://crimestoppers-uk.org/give-information/forms/give-information-anonymously
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