Police said they had received more than 60 calls after a television appeal for information over missing chef Claudia Lawrence.
Detective Superintendent Ray Galloway, of North Yorkshire Police, said officers were working on new lines of inquiry after the appeal for current and former partners of Claudia shown on BBC1's Crimewatch on Wednesday night.
Miss Lawrence, 35, was last seen near her home in York on March 18, and did not arrive for a 6am shift at a University of York kitchen the following morning.
North Yorkshire Police have now classified their investigation into her disappearance as one of suspected murder.
Mr Galloway said Miss Lawrence was involved in relationships of "complexity and mystery", and kept those relationships secret from friends and family.
He said: "I am very pleased with the response to the primary appeal to trace Claudia's partners both from her past and present. The investigation team is now following up these new lines of inquiry.
"I strongly urge anyone who has had a relationship with Claudia, but has not yet come forward to the police, to make contact as soon as possible. If the person wishes to do this discreetly and in confidence then we are happy to assist."
Wednesday night's appeal, nearly 11 weeks after Miss Lawrence went missing, showed reconstructions of her last known movements and interviews with her father, sister and closest friend. Miss Lawrence's family had previously dismissed speculation that she might have had a secret boyfriend.
But Mr Galloway said: "As the investigation has developed, it's apparent that some of Claudia's relationships had an element of complexity and mystery to them. I am certain that some of those relationships were not known to her family or her friends."
He continued: "I'm not here to judge Claudia's relationships, I'm here to investigate them. I need people to share that information with me."
