Police say they have made a “significant breakthrough” in their investigation into the death of Karen Ristevski, after they finally tracked down and interviewed a witness who had contacted them more than four months ago.

The development prompted another search for clues in an area near where her body was found, north-west of Melbourne.

Detective Inspector Tim Day, who heads Victoria Police’s missing persons squad, said the witness saw a man alone in a black Mercedes Benz, similar to one owned by Ms Ristevski, around the time of her disappearance in June last year.

The car, seen in the Childers Road and Mount Macedon Road area, was on the wrong side of the road about 1.5 kilometres from where her body was found in February.

“The witness has seen the vehicle in the last week of June. We’re trying to narrow down exactly what day it was,” Detective Inspector Day said.

“We’re obviously working towards whether or not it was actually on the day that Karen went missing.”

The identification of the witness, and the information they provided, represented a “significant breakthrough” in the case, he said.

“I can confirm that that observation was articulated prior to the discovery of Karen’s body,” Detective Inspector Day said.

“We [have] only … been in a position to speak to the witness in the last week or so.”

Police want to speak to anyone who saw a car like this one in the Macedon area on the day Ms Ristevski disappeared. Photo: AAP

‘Starting point’ for new search

The 47-year-old was reported missing on June 30, 2016, after being last seen at home by her husband Borce Ristevski the day before.

Ms Ristevski’s disappearance was described as “highly irregular” at the time and happened after an argument with her husband.

Her body was found in bushland in the Mount Macedon Regional Park on February 20 after months of searching, including around the river near her Avondale Heights home in Melbourne’s north-west, 50 kilometres from where her body was found.

Police also searched properties at Toolern Vale and Gisborne, about 30 kilometres from the Macedon site, in December.

Detective Inspector Day said the information from the witness provided police with a “starting point” for a new search by SES volunteers along the roadside from Childers Road to where the body was found.

“This is about the sighting of this vehicle, the search of the roadway and making an appeal to the public if they’ve seen anything suspicious in this area to call Crime Stoppers,” he said.

In June, police released CCTV footage of a black Mercedes Benz seen by witnesses.

At the time, police said a number of witnesses had told them about seeing the car in the Diggers Rest, Toolern Vale and Mount Macedon area on the day she went missing.