Claudia, who disappeared nearly four years ago, would have marked her 39th birthday today, February 27.
But instead of celebrating her family have been left with just memories – and the continuing mystery of exactly what happened when she vanished.
Claudia was on her way to work at York University from her home in the city when she disappeared on March 18, 2009.
Police suspect she was murdered, but despite a huge investigation which has even taken them overseas no trace of her has ever been found.
Her father Peter Lawrence’s close friend and spokesman Martin Dales said: “I cannot believe that we are yet again at another birthday for Claudia and there is still no news as to what has happened to her.
“All anniversaries are hard for the family and friends to cope with and it is unacceptable that there is still no closure – good or bad.
“Out there are some heartless persons who know something but they don’t have the guts to tell the police what they know. How low can people get? It’s outrageous and continues, after four years, to cause immense damage to Peter and the family.”
He added: “Vast amounts of police time, effort and over £750,000 of public money has gone into trying to find answers and, after this length of time, they, along with family and friends, deserve to have those answers.
“So I make a further appeal to those who know these answers.
“How can you sleep at night knowing you know the answer?
“How can you live the lie with yourselves?
“Have you no feelings for those who are suffering because of your misguided silence?
“Do what you know in your heart of hearts what is right and end the misery of all those who love and care for Claudia even if you don’t.”
Claudia and her family originally came from Darlington and later moved to Malton, North Yorkshire, where she was brought up.
Anyone with information that could help the investigation, can phone police on 101 or Crimestoppers on 0800-555111.
More Crime News