Police said they hope a small circle of people known to a woman will speak to officers, 20 years after she vanished.
Kellie Pratt, who was 28 and a sex worker, was last seen outside The Rose pub in Queens Road, Norwich, on 11 June 2000.
Her body has not been found, nor has a link with Steve Wright who murdered five women in Ipswich in 2006.
Norfolk Police's cold case manager Andy Guy said: "It may be that those who knew her did not tell us everything."
He added: "There are people who have turned their lives around and are completely unrecognisable from 20 years ago and there is a possibility they will talk now.
"People who may not have been honest with us in 2000, we want to hear from them."
Ms Pratt, who was from Newcastle, was called on her Nokia 6100 at 23:30 BST - within about 10 minutes of being seen outside the pub - and said she was with "a punter".
Police spoke to the "associate" who made that final call to Ms Pratt but the client she was with has remained unknown and no clues were found during a search of her accommodation in Loddon.
"We have never found Kellie and we've never found her phone," added Mr Guy, who said her disappearance was listed as a homicide case.
"The person she was with that night may or may not be responsible but if he wasn't we would still want to hear from them."
Ms Pratt's disappearance fell within a timeline of three murders of women working in Norwich's red light district.
The cases were reinvestigated when Philip Stanley was convicted in 2005 for the murder of Norwich prostitute Hayley Curtis, who went missing in 2001, and when Wright was found guilty of the Ipswich murders in 2008.
"There have been several lines of inquiry over the years," said Mr Guy.
"We had information which led us to search several areas with cadaver dogs, but nothing came of that.
"Some cold cases we have a call maybe once a month - it's not like that with Kellie.
"She was working on the street and had a chaotic lifestyle and she didn't know lots of people in Norwich, it was quite a small bubble she was involved with.
"The problem we had is that no one was going to say they had used her services.
"With no body and no DNA evidence we are relying on people coming forward."