Missing persons squad detectives are focusing their efforts on a "rural area" to the north-west of Melbourne, Acting Sergeant Melissa Seach said on Thursday.

Police would not disclose a specific location.

"Investigators are appealing for anyone that resides in this area to consider checking their properties for any changes or any suspicious activity since the disappearance of Karen," Sergeant Seach said.

Mrs Ristevski, 47, was last seen on June 29.

Her husband Borce Ristevski said the couple had an argument over financial issues before she left their Avondale Heights home to go for a walk to "clear her head".

Detectives are investigating if she was murdered.

Police have already searched several locations, including the Maribyrnong River behind the family's home and nearby parkland.

Mr and Mrs Ristevski have one daughter, 21-year-old Sarah.

In the last public appeal the family made on July 14, Mrs Ristevski's aunt Patricia pleaded for help.

"We have nothing, so if you have something that you know, something that you have seen, you've heard something, someone has spoken to you about something, anything, please, we're asking you to help us," she said.

"It's not possible for someone to just disappear. It's not Karen, Karen would not leave us."

Mrs Ristevski is about 160 centimetres tall with a slim build and shoulder-length brown hair.

She was last seen wearing a black jacket and jeans and it is believed she was carrying a Coach handbag and purse.

Police said anyone who has seen Mrs Ristevski should contact Triple 0 or anyone with information should contact Crime Stoppers on 1800 333 000 or submit a confidential crime report.