Christos was last seen on Big Muster Drive, Dinner Plain, northeast of Melbourne, around 2:45 pm on Friday.
It is understood that he went for a walk to see emus in the area, but has not been seen since.
“By 6pm that night he hadn’t returned, so his wife contacted us and was worried that something might have happened,” said Inspector Paul Hargreaves.
“He doesn’t know much about the area, but having said he was just walking on a local trail, the mountain trail as it’s called, is where we believe he went.
“What we understand is that Christos is quite suitable for his age, he walks approximately 45 minutes every day with his dog, he is a mobile person and in good health.
“We’re thinking that he might have had some misadventure or something happened to him, maybe he got disoriented, we don’t know.”
Emergency services have been looking for Christos for the past two days.
Hargreaves said a witness told SES on Friday night that he saw a man who matched his description.
“They’ve seen an elderly gentleman that meets the description or fits the description of Christos and we’re really looking forward to hearing from that person,” he said.
“They provided some brief details to an SES researcher who was away at the time, we believe the witness will likely stay in Dinner Plain and we are slamming some doors at the moment.”
Christos was last seen wearing a long-sleeved top, long-sleeved sweater, pants, and crocs.
“What we know at the time, he was wearing a pair of white jeans and shoes and a dark or black colored sweater, he is bald and weighed about 65 pounds,” Hargreaves said.
Officials are worried about Christos as temperatures are low and windy.
“We know we have a limited window and conditions can be quite dangerous,” Hargreaves said.
Anyone with information about Christos’ whereabouts should contact Crime Stoppers on 1800 333 000.