Several items belonging to missing Auckland mother Carmen Thomas and her car are unaccounted for, say police, who describe her disappearance about a month ago as sinister.

Ms Thomas, described by police as an escort, was reported missing on July 13 after she failed to collect her five-year-old son. Her Nissan Pulsar car (registration number ATS 209) was reported as abandoned in Hamilton on July 5, and there have been no corroborated sightings since footage of her at an Auckland supermarket on June 27.

Her car had a temporary spare left rear tyre when recovered in Hamilton, but the car's standard tyre and jack equipment have not been found, Detective Inspector Mark Benefield said.

"Further, the turquoise-coloured handbag that Carmen always used was not in her car or her home when police searched it.

"Car keys are also unaccounted for.

"We'd very much like to know where these items are," said Mr Benefield.

Cash, an overnight bag and a child's car seat were in the vehicle.

Ms Thomas' bank accounts had not been touched, and she had not contacted family or friends.

"We have to acknowledge that things are looking pretty sinister at this stage of the investigation," he said.

"Given that she has a five year-old son who is missing her and that her mother has travelled from South Africa to help find her, one could reasonably assume that, if she was alive and well, she might have tried to contact police or her family."

Ms Thomas' three-door car was parked in Auckland's Sylvan St East for several hours from just after midnight on June 26, and police wanted to hear from anyone who noticed it there.

"We believe she was driving around the Newmarket area with four 'normal' tyres on June 25, so we'd love to hear from anyone who can tell us when the tyres were changed, where the standard tyre is and what was wrong with it," Mr Benefield said.

The investigation into Ms Thomas' disappearance features in tonight's episode of Police Ten-7 on TV2.