Point Cook woman Samantha's grey Kia Sportage broke down on the Princes Highway in Tamboon, in Victoria's north-east, at about 8.15am on Friday, April 26, police were told.
It's believed a passer-by stopped to offer help, and Samantha has not been seen since.
Police and Samantha's family are concerned as this disappearance is out of character.
Samantha also has a medical condition that has prompted worries for her welfare.
She was last seen wearing a blue/grey fleece top, jeans and running shoes.
Investigators believe Samantha was trying to travel to Melbourne and may have been hitchhiking along the Princes Highway after her car broke down.
Anyone who sees Samantha is urged to contact Bairnsdale Police Station on (03) 5150 2600.
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