Police told the family of a missing southern Ontario woman to expect the worst on Thursday, as the investigation into her whereabouts stretched into the fourth day.

Sonia Varaschin, a 42-year-old nurse from Orangeville, has been missing since Sunday. On Monday morning, police found her white Toyota Corolla abandoned and stained with blood.

"We're always going to maintain hope but at this point we're preparing the family and ourselves for the worst," Ontario Provincial Police Det.-Insp. Mark Pritchard told reporters.

On Thursday, police again asked the public to come forward with any potential information about Varaschin's whereabouts. However, despite widespread media coverage, there has yet to be a major break in the case.

On Wednesday, police said that foul play was a definite possibility in the case, which has shocked the small community of Orangeville.

Police have also zeroed in on a minivan which was spotted near the back lane where the Corolla was found. The minivan was captured on security cameras, and police believe the driver may have witnessed something related to Varaschin's case.

The back lane is near the town hall in Orangeville, which is about 80 kilometres northwest of Toronto. Bloodstains were also found inside and outside of Varaschin's nearby home.

Meanwhile, police have asked residents in rural areas to check around their properties for any clues about the disappearance.

"There's a long weekend coming, people are going to be out and about and we really need the public to be our eyes and ears and help us locate Sonia," said Pritchard.

Varaschin was reported missing after she failed to show up for her job at a pharmaceutical company in Mississauga on Monday.

Extensive ground and air searches have thus far been unable to turn up any clues in the case, and police have interviewed several potential witnesses.

However, no suspects have been named.