The 88-year-old was en route to Scotland to speak at a regimental dinner when the items vanished. He boarded the Plymouth-to- Glasgow Central service in Alnmouth at 2pm on Friday March 7 and placed his case in the luggage rack.
The case contained a miniature France and Germany Star and a 1939-1945 Victory Medal, along with gold cufflinks - engraved with the initials CSP - which were given to him as a wedding present 60 years ago.
The train stopped at Berwick upon Tweed, Edinburgh Waverley, Edinburgh Haymarket and Motherwell before arriving in Glasgow at 5.30pm, at which point the man discovered his luggage was missing.
British Transport Police said CCTV footage had not identified the culprit and the items had not been handed in to lost property.
Officers are now liaising with local pawnbrokers and monitoring auction sales.
Detective Constable Lorna White said: "It would be of great comfort to the gentleman if the items were returned to him safely. However, our extensive enquiries have failed to trace them. Anyone who is offered medals or cufflinks in unusual circumstances and can help our enquiry is urged to contact BTP.
"I am also appealing for anyone who was on the train between Alnmouth and Glasgow and saw anyone acting suspiciously or remove the small black case to get in touch."