THE father of missing academic Fergus McInnes has made an emotional appeal for help in finding his son.

In an online plea on a web page set up by family and friends, Bennet McInnes said the search continues for the 51-year-old Edinburgh University fellow, who went missing on a trip to Switzerland three weeks ago.

He wrote: "We are hoping for a good outcome, but there is much that is bad in the present situation."

Police Scotland have been working with their counterparts in Switzerland and Interpol in trying to trace the computer expert, who has a history of mental illness.

Mr McInnes said the family has tried to find possible answers to his son's disappearance, adding: "I cannot rule out the suggestion that he has taken time out by deliberately going missing, but this seems highly implausible to me.

"Was he mugged, either in Geneva Airport or on the train? We know that he had not slept much during the night of September 8/9 before he went to Edinburgh Airport and a possibility being considered is that he fell asleep on the train out of Geneva, failed to come off at Martigny, and ended up at a strange station.

"He is short-sighted and always wears glasses. If he lost his glasses, he would be disoriented and upset.

"If he has suffered a traumatic experience he may have lost his memory as well as his identification.

"If something like that has happened to him we hope that he is being looked after by friendly people."

His sister, Lorna McInnes, said earlier the keen hillwalker may have decided to trek five miles from Martigny to a museum in the village of Salvan dedicated to Nobel-prize winner Guglielmo Marconi.

Friends said online that Mr McInnes had been on a "manic high" in recent weeks, saying he was in good spirits when he left and adding: "Did something happen during his journey that made him take a sudden dive into depression?"

Police Scotland said officers were concerned over the disappearance.