The mother of Claudia Lawrence said “if you give up on hope you might as well give up altogether” as she marked the 13th anniversary of her daughter’s disappearance.
Police believe Claudia was murdered, although no body has ever been found.
The 35-year-old was last seen on March 18 2009.
Her mother, Joan Lawrence, told BBC Radio York today (Friday): “I can’t believe it’s 13 years. It shouldn’t be.
“We should really have had answers before now.”
Police activity around the case increased last year when the North Yorkshire force spent two weeks searching a lake and nearby woods at Sand Hutton just outside York.
Officers later said that “nothing of obvious significance” was found.
Mrs Lawrence said: “I have had hope so many times and it’s been dashed.
“I never give up on hope. If you give up on hope, you might as well give up altogether.”
She said: “It’s the not knowing. Despite the fact she was 35, she is my child.
“You can’t say goodbye, you don’t know whether she’s dead, you don’t know if she’s alive, you don’t know where she is, you don’t know what’s happened to her, there’s no grave.”
Mrs Lawrence said: “It’s still pretty awful, it really is.”
Trying to solve the mystery
She said she is continuing to try and solve the mystery for herself and is reviewing what happened “with a fine-toothed comb” for “simple things that have been missed”.
North Yorkshire Police has conducted two investigations and questioned nine people in relation to her disappearance and suspected murder, but no charges have ever been brought.
Speaking after he took over as senior investigating officer in the case last year, Detective Superintendent Wayne Fox repeated the belief that several people know, or have suspicions about, what happened to the University of York chef.
He said some of the information received by the force “appears extremely interesting and sparks a whole new line of investigation”, and he urged anyone providing this information to get back in touch.
Ms Lawrence’s father, Peter, died last year without knowing what happened to his daughter.
He had campaigned to get answers to the puzzle of her disappearance and spent years arguing for what became the Guardianship (Missing Persons) Bill – also known as Claudia’s Law – which allows relatives to take control of their missing loved ones’ financial matters.
If you have any information that could assist the investigation, please contact North Yorkshire Police on 101, select option 1, and pass details to the Force Control Room quoting “Claudia Lawrence”.
If you would prefer to remain anonymous, please pass information to the independent charity Crimestoppers on 0800 555 111 quoting “Claudia Lawrence, North Yorkshire Police”. A report can also be made online at www.crimestoppers-uk.org.