Ms Shaw said Mr Gourlay was last with the family on December 18 to celebrate the birth of a grandchild and was at a friend's home the day he went missing.
''It was not until December 23, which is dad's birthday, when we noticed (sic) something could be wrong as he failed to get in contact with us.''
The family reported him missing on Christmas Day.
''This is a very stressful time for us as a family. It is so unlike dad to wander off like this. It really is a needle-in-a-haystack search.''
Ms Shaw said police and Land Search and Rescue had been ''incredible'', and she thanked all who had helped in the search so far.
Mr Gourlay is described as Caucasian, about 173cm tall, of slight build, with short grey hair, grey facial hair and a sleeve tattoo on his forearm. He has a slightly lazy eye.
It was thought Mr Gourlay was on foot as the work van, his car, bicycle and motorcycle were all accounted for.
Anyone with information which could assist police was asked to contact the Southern District Command Centre on (03) 471-5002(03) 471-5002.