The York chef was last seen on CCTV on her way home from work at the University of York on March 18 2009.
The alarm was raised after she failed to arrive for her 6am shift the next day.
A murder investigation was launched a month later but no-one was ever charged and nearly 11 years on, her disappearance remains a mystery.
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Martin Dales, a friend and spokesman for Claudia's father, Peter Lawrence, said: “In Peter’s mind Claudia is ever-present in his thoughts and prayers even though he hasn’t had her around him for nearly 11 years. The pain of such a long absence does not go away: it is not something you get used to but rather manage whilst getting on with living day-to-day and waiting.
“Clearly someone has the knowledge of where Claudia is and is living with the secret that is causing such anguish for Peter and the family. Truth will out at some point and the sooner the better for the family, friends and police.”
North Yorkshire Police said last year they would never give up on Claudia.
Anyone with information is asked to call 101.