The detective in charge of the search for missing university chef Claudia Lawrence voiced fears today that she may have come to harm after meeting up with someone she knew.
Detective Superintendent Ray Galloway said it was "extremely rare" for someone to be abducted from the street by a stranger.
He was speaking a week after Miss Lawrence was last seen leaving work at the University of York.
He said it was possible that the 35-year-old had met up with someone the night before she disappeared.
"My focus is on the people that she knew," he said.
"She would not have got into a vehicle that she didn't know and she wouldn't have gone to meet somebody that she didn't know," said Mr Galloway.
"I believe that Claudia is with or has gone with somebody that she knows."
He said Miss Lawrence spoke to her parents last Wednesday evening and exchanged mobile text messages with two friends.
The next day her phone was switched off or powered down and has not been located.
Mr Galloway said: "She was a prolific texter. We have now gone through Mother's Day. She was somebody that was always in contact.
"She was very, very social. She was speaking to her friends and family all of the time.
"That stopped around about 8.30 on Wednesday evening. Why did that stop? I must be concerned that she has come to harm."
Police today released CCTV footage of Miss Lawrence arriving and leaving Goodricke College, where she worked, last Wednesday.
As she was walking home, she was picked up by a colleague and dropped off at her home in Heworth.
"Seven days on I am extremely concerned," Mr Galloway said.
"My professional judgment is that Claudia has probably come to harm."
He said that, while police had no "tangible" evidence of a crime, there was no reason to believe that Miss Lawrence had harmed herself as she was not depressed and had no financial problems.
He said police were focusing the investigation on people Miss Lawrence knew and appealed to anybody who knew of any relationship she might have had in the past.
He continued: "I would appeal to anybody who knows of a historic relationship or association she might have had with somebody and that's where it will lie."
Miss Lawrence did not appear on any CCTV footage from her normal route to work on Thursday morning, the detective said.
Mr Galloway said North Yorkshire Police were bringing in officers from other forces to help with the search but the focus of the investigation was still on York.
Friends and family described Miss Lawrence as a "creature of habit" and said her disappearance was "totally out of character".
Making a television appeal for her friend's return, Suzy Cooper said: "Claudia's a very sociable and popular person. Everybody likes her and she likes everybody.
"She's a very sweet-natured girl and she's also a creature of habit. She's not someone that's spontaneous and would just flit off somewhere, so the whole thing is totally out of character for her."
Yesterday, Miss Lawrence's father Peter, a solicitor from Slingsby, North Yorkshire, walked part of her route to work, handing out posters appealing for the public's help to find his daughter.
He described Miss Lawrence's disappearance as a "living nightmare".
Her mother, Joan Lawrence, of Norton, North Yorkshire, said she had offered her daughter money for a taxi to work but she turned it down as she "liked walking for the exercise".
Police said Miss Lawrence had no money, bank cards or passport with her when she went missing.
She is described as white, around 5ft 6in and of slim build, with brown hair and brown eyes. She was last seen wearing a white T-shirt, blue skinny jeans and white trainers.
Police are appealing for help to find the small blue or green rucksack which Miss Lawrence used to carry her chef's whites to work and was believed to have with her when she disappeared.