Jeffrey Boucher, a 52-year-old high school teacher, went for a run at around 6 a.m. Monday and hasn't been seen since.
"I don't know what happened this morning," his wife Kristen told CBC News. "He didn't give me a kiss goodbye and he didn't leave for work. He's never taken a sick day in 25 years. When he didn't come home, alarm bells went off.
"He's been a good husband and a good father. He cares for everybody."
"Could this be a midlife crisis of some kind where something bothered him at work and he just wants to run away? I don't know."
Boucher left behind his wallet and his car is still in the garage.
The police are using ATVs and a K-9 unit to carry out the search.
Boucher typically ran 10 kilometres and often varied his route, sometimes running in green spaces in the area.
"It's ramped up to an intensive search," said Durham Regional Police Insp. David Brown. "It's a hazardous situation with this snow and ice and we are fearful he may have tripped and fallen and is in a wooded ravine area," he said.
Police have set up a command post near the Boucher family home on Gilchrist Court, near Brock Street and Taunton Road.
Boucher is white, six feet tall, weighs 180 pounds with grey and white short hair.