Seven years on from the disappearance of Claudia Lawrence, her mother has said she thinks she is alive and "being held somewhere against her will".
The chef from York, North Yorkshire, went missing on 18 March 2009 at the age of 35.
It was recently revealed that four men held as part of the police investigation would not face charges.
Speaking to BBC Look North, Joan Lawrence said: "I have no instinct whatsoever that she isn't alive".
Her comments come on a legal milestone which states a person may be legally declared dead after being missing for seven years.
The previously arrested men, who are all in their 50s and from the York area, were held last year as part of a review of the initial investigation into the case.
North Yorkshire Police said up to 20 detectives and police staff had worked full-time on the review for more than two years at a cost of nearly £800,000.
Officers believed the investigation had been compromised by the "reluctance of some, and refusal of others, to co-operate" with the force.
Mrs Lawrence said she was constantly surrounded by "reminders" of her daughter, whatever she was doing.
She said: "Sometimes I feel like I'm banging my head against a brick wall, but I get through every day.
"There's somebody out there who knows something, but I have no instinct whatsoever that she isn't alive, I've had no cut-off feeling at all.
"In my opinion she's being held somewhere against her will and I want people to imagine if it was their child, how would they feel?"
Claudia Lawrence disappearance timeline
- 18 March 2009 The last sighting of Miss Lawrence as she walks back to her house after a shift at work
- 19 March 2009 Police are informed of her disappearance after she fails to meet a friend for a pre-arranged drink at a pub
- 23 March 2009 Her father Peter Lawrence appeals for information about his daughter at a press conference in York
- 25 March 2009 CCTV footage of the chef's last known movements are released
- 24 April 2009 Detectives say they are treating Miss Lawrence's disappearance as a suspected murder investigation
- 6 May 2009 Police reveal they have received more than 1,000 calls about the disappearance and had taken 1,096 statements
- 6 May 2010 Mr Lawrence calls for an urgent independent inquiry into the police investigation
- 29 July 2010 Police confirm they are scaling back the number of officers dedicated to the inquiry
- 29 October 2013 Police announce that a new forensic search of Miss Lawrence's home is to begin as they launch a fresh review of the case
- 13 May 2014 A 59-year-old man is arrested on suspicion of murder. He is later released without charge in November
- March-April 2015 Four men are arrested on suspicion of murder and released on bail
- 8 March 2016 Police say the Crown Prosecution Service has decided the four men will not face charges
About 100 police officers were dedicated to the investigation at its height, but the figure has since dropped.
Martin Dales, a friend and spokesman for Miss Lawrence's father Peter, said: "It seems that we're all back to square one.
"It's really quite depressing especially as someone is clearly withholding the information needed."
A North Yorkshire Police spokesman said: "The investigation team will continue to thoroughly assess any new leads and information.
"We remind those who we suspect are withholding key information about Claudia that we will not give up our quest to find the truth."