Charlene Lever, 21, of Wallace Street, Port Glasgow, was last seen by a family member at her home on Thursday, July 17.
Since then there have been a number of sightings of her in the local area.
However, there have been no further sightings of her since Saturday, July 19 and her family and friends are becoming increasingly concerned for her safety.
Charlene is described as white, 5ft 4 in and of slim build with light brown hair and blue eyes. When she was last seen she was wearing a red tracksuit.
Inspector Steven Espie is appealing for information.
He said: "Despite previous appeals in the local area and extensive police inquiries, we have been unable to trace Charlene.
"I would urge anyone with any information on her whereabouts, or indeed Charlene herself to contact Police Scotland on 101."