Police officers are searching the River Ouse in York after missing Wetherby student Megan Roberts was spotted on CCTV next to the water.
As concerns grow for the 20-year-old, North Yorkshire Police have been studying CCTV footage of her usual way home - as confirmed by friends - and alternative routes she could have taken.
They have not managed to find the fine art student on camera on one of these routes back to her home in the Clifton area of York, despite checking the tapes until 4am.
The former Wetherby High School pupil was spotted on CCTV footage with friends on one side of Lendal Bridge at 2.10am. The group she was with were seen by the camera on the other side of the bridge at 2.20am - but Megan was not there.
In a press conference, Superintendent Phil Cain said they had deployed underwater search parties who are currently skimming the surface area of the River Ouse between Scarborough Bridge and Skeldergate Bridge.
He said: “We currently have two dedicated search teams involved in the search, which is about 30 members of staff.”
Police added they had no evidence to suggest the student, who has a younger brother and sister, was intoxicated when she went missing.
“There is nothing suspicious to report of her disappearance at the moment.
“Megan’s disappearance is extremely unlikely and thus adds to our concern.
“I would appeal for anyone who has any information at all to get in touch with the police using the 101 number.”
At the press conference today (Tuesday) Superintendent Cain reiterated the police appeal for information.
He said: “We are very concerned for her welfare and urge the public to come forward if they have any information on her whereabouts.”
Police have added that special family support teams are accompanying Miss Roberts’ family in Wetherby.
“We’ve got family officers deployed with the mother, and we are also in touch with Megan’s father.
“Megan’s family have stated they just want her to come back safe and well.”
Messages posted on Megan’s Twitter account suggested her and a friend were being “stalked” by an unknown male six nights before she disappeared in the city centre.
She posted that a man was following them from pub to pub. Her friend Rockie Thorley also commented on the “creepy guy” bothering them.
One message by Rockie Thorley, retweeted by Megan, said: “The bar staff have just noticed our stalker and come to tell us that they won’t be serving him anymore and not to worry we are safe”.
Messages were also posted regarding Megan reviewing text messages from an unknown number.
On Wednesday she wrote: “Will never understand why some men continue to message random girls without a reply...”
Police said they are aware of all messages but stressed they are not linking them to her disappearance for the time being.
A police spokesman also said they were not linking her disappearance with that of university chef Claudia Lawrence, who vanished five years ago in York and is believed to have been killed.