The mother of missing Auckland woman Carmen Thomas last night spoke of her grief, as police revealed new details of items missing from the 32-year-old's car.

"We have to acknowledge that things are looking pretty sinister at this stage of the investigation," said inquiry head Detective Inspector Mark Benefield.

Ms Thomas' mother, Teresa Scott, has travelled from South Africa to help in the hunt for her daughter and spoke publicly for the first time last night.

"I broke down and cried myself to sleep on a few nights," she said.

"I cried at work. I just want her to come back safe and sound. I just want her to come back."

She described her daughter - mother of a five-year-old boy - as fun-loving, vivacious and friendly.

"She's a good mum. She's not the kind of person who would just leave her son."

Mr Benefield last night revealed that Carmen's dark Nissan Pulsar three-door hatchback had a "space saver" temporary left rear tyre when it was discovered abandoned in Hamilton on July 13.

The car's standard tyre and jack equipment were missing - with Ms Thomas' turquoise-coloured handbag and car keys.

Mr Benefield said it could be reasonably assumed that if Ms Thomas was "alive and well" she might have tried to contact police or her family.

"Carmen's bank accounts have not been touched, and she has not had any contact with family or friends since July 1 at the very latest, possibly earlier.

"We've had no corroborated sightings of her since June 27 when we know she shopped at the Greenlane Countdown supermarket."

Her car was parked in Sylvan St East for several hours from shortly after midnight on June 26 and police want to hear from anyone who noticed it there, particularly if they noticed what wheels it had.

"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.

Ms Thomas' family yesterday issued a "plea from the heart" to her "abductors".

Her aunt, Carol Lavagna, posted a message on the missing woman's Facebook site, begging for her return.

"We are not in a financial position to bargain if this is what you are holding her for. We are ordinary people living ordinary lives and this is just so extreme, what the hell is it all for/about?"

Friend Natalie Ireland asked the "vulgar monster" who knew where she was, "How do you sleep at night" and "How do you look in the mirror".