Claudia's friends targeted in hate campaign

The nature of the online abuse has escalated to such an extent that a message board on the findclaudia.co.uk website has had to be closed down.

The revelations that friends of the missing York University chef have been the victims of abusive comments on the site emerged yesterday at a press conference to mark the 13-month anniversary since she vanished.

Martin Dales, a friend and spokesman of the missing woman's father, Peter Lawrence, condemned those responsible for the abuse, although he would not be drawn on specific details of exactly what had been posted online.

However, it is understood that the abuse made references to Miss Lawrence's tangled love life after detectives revealed that she had embarked on affairs with married men.

But some of the most sustained abuse is thought to have been specifically directed at Miss Lawrence's closest friends, including Suzy Cooper and Jen King.

The website was launched in May last year in the hope of triggering new information to trace Miss Lawrence, and Mr Dales stressed that the majority of the 6,000 messages which had been left on it had been supportive.

He added: "The website has proved to be a very valuable tool to let people find out what is going on as well as for bringing in information.

"Regrettably we have had to take it (the message board) down because it was being hijacked by evil people who seemed determined to pull down some of Claudia's friends and have a go at her family.

"In the end it got to the point where it was grossly unfair to have that particular situation going on. It is a shame because some people left messages that were a huge support to the family.

"It is desperate, and I find it difficult to believe that people can stoop this low to hurt people who care and love Claudia so much."

It also emerged yesterday that Mr Dales had received a series of tip-offs from the public about four separate locations on the outskirts of York which he has written to North Yorkshire Police about.

Mr Dales has visited the locations himself but has yet to hear back from officers to establish if searches have been conducted.

He urged detectives to provide a greater degree of transparency in the investigation to reassure the public that potential leads are being pursued – and also to instill greater confidence in the police to help generate new leads.

Mr Dales, who lives in Old Malton in North Yorkshire, said: "It is obviously heartening to know that information is still coming in, but the police need to be aware that it is a two-way relationship with the public.

"They will obviously not be able to disclose everything for operational reasons, but the public do want to know that the pieces of information that they are providing are being followed up, even if nothing comes of it."

However, the officer leading the inquiry, Detective Superintendent Ray Galloway, maintained that all information is being considered by the investigation team before a decision is taken to act on any potential new leads.

Mr Galloway also confirmed that Miss Lawrence's family are being kept "fully updated" with any developments.

Miss Lawrence was last seen walking near her Heworth Road home in York after finishing work on March 18 last year. Police upgraded the inquiry to a murder investigation the following month.

One of the biggest recent developments emerged last month when detectives revealed that Miss Lawrence had told a friend she had been out with a mystery boyfriend until the early hours of March 17, 2009 – the day before she was last seen alive.

Det Supt Galloway confirmed yesterday that the link to the mystery boyfriend remained an "active and positive line of inquiry".