Tammy Lisa Dyson, also known as Tamela Menzies, was 23 when she was last seen in Currumbin in 1995.
Ms Dyson had moved to Brisbane from Victoria in 1988, working in the adult entertainment industry in southeast Queensland.
She used the name "Pebbles" in her work and associated with criminals who were known to police at the time.
In an emotional appeal on Wednesday, Ms Dyson's sons Jyles Lebler and Rainey Lebler asked for anyone with information to come forward.
"We were only little boys when our mum disappeared and we have wondered what happened to her for all our lives," Jyles Lebler said.
"Our grandmother who raised us has never given up trying to find out what happened to her daughter."
Ms Dyson's sister Olivia told police that in 1995 Ms Dyson had called her sounding distressed.
She said she picked up Ms Dyson, who looked as though she had been assaulted, and drove her to drug rehabilitation centre the Currumbin Clinic.
Ms Dyson was checked out of the clinic a few days later by an unknown woman who said she was her sister.
Ms Dyson was checked out of a rehabilitation clinic by a mystery woman before she disappeared. (HANDOUT/QUEENSLAND POLICE SERVICE)
Police have never been able to identify the woman.
"Tammy associated with criminals that were known to police and vanished without a trace after giving custody of her children and possessions to her mother; we believe the circumstances of her disappearance is suspicious," Detective Senior Sergeant Tara Kentwell said.
The day after Ms Dyson was checked out of Currumbin Clinic she signed a statutory declaration giving custody of her children and all her belongings to her mother, Loretta.
Ms Dyson has not been seen or heard from since.
"She wouldn't just disappear and leave us two behind," said Rainey Lebler, who was just one year old when his mother disappeared.
"She really loved both of us so I just find it really hard to believe she would've just disappeared by herself."
There have been a number of unconfirmed sightings of Ms Dyson, including information that she had moved overseas.
Police are urging the person who checked Ms Dyson out of the Currumbin Clinic or anyone who has any information about her disappearance or whereabouts to come forward.
"There are people out there with information," Sen Sgt Kentwell said.
"Tammy's family and her two boys deserve answers, so if you know something, please come forward."
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