British-born Margaret Nancy Sarnek, nee Pyatt, went missing from her George Town home in 1975.
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"She disappeared one night from home and she didn't even have her coat or purse," Mrs Blair said.
Mrs Sarnek, who went by her second name Nancy, had three daughters Patricia, then 12, Jadge, then 17, and Misha, then 18.
The sisters said the police received a few sightings of their mother on the Bass Highway and there were suggestions she might have been going to catch a ship.
"She was so strong and family orientated having come from such a big family with 10 other siblings," Ms Sarnek said.
Mrs Sarnek was the only one of 11 children in Australia and there were suggestions she might have gone back to England.
"Dad died almost four years ago, but he used to ring all around the world trying to find out what happened to her," Mrs Blair said.
"Not knowing is the hardest part. She would be 70 in two days."
The sisters were prompted to speak out again about their mother's disappearance after a Sydney woman missing for 32 years was found.
Mrs Sarnek's case will be broadcast on national television tonight at the end of the show Without A Trace.
Ms Sarnek was hopeful the exposure might lead to finding their mother, but Mrs Blair was not as optimistic.
"It's been too long. I don't think she's alive anymore - I don't think she survived that first night," Mrs Blair said.
"Whether it was foul play or an accident I don't know," she said.
"I still hope," Ms Sarnek replied. "I have no idea what happened to her but someone must have seen her."
Mrs Sarnek moved to Australia from Wolverhampton in 1967 with her Polish-born husband Tad and the three girls.
Insp. Paul Reynolds, of George Town police, said he had reviewed the file and would meet with the sisters to see if there was anything else police could do.
"It's a very cold case and there has been no additional information and no new leads," Insp. Reynolds said.
Mrs Blair said she reads the death notices in the papers and when she sees women with similar ages or names she wonders if that was her mother.
"I'd always like to know what happened even if she doesn't want to know the family anymore," she said.
"You never know. A lot of people are gone from back then but there might still be someone who knows something but was too scared to say anything."
Anyone with any information, no matter how trivial, can contact the National Missing Persons Unit on 1800 000 634 or Crime Stoppers on 1800 005 555.
MISSING MUM
Name: Margaret Nancy Sarnek, nee Pyatt.
Date of birth: February 10, 1935.
Last seen: 84 Franklin St, George Town.
Reported missing: August 26, 1975.
Description: 157cm tall, slim build with greying hair, green eyes and a scar on her left temple and cheek. She spoke with an English accent.