Police trying to trace a 17-year-old girl missing from her home in Shropshire since Sunday say they feel she "may have come to harm".
Georgia Williams, from Wellington, is believed to be in Glasgow where a 22-year-old man was arrested earlier on suspicion of kidnap. Her disappearance is said to be "out of character".
She is the daughter of a West Mercia Police detective constable.
Officers in Scotland have been searching two addresses in Glasgow.
West Mercia Police and Police Scotland said they were holding a joint operation at an address in Dunblane Street, in the Cowcaddens area, and at the Premier Inn, West Nile Street, in the city centre.
A property in Avondale Road, Wellington, has also been searched for a second day by forensics officers.
The man, also from Wellington, was arrested at the hotel and is being questioned in Glasgow.
Investigating a tweet
Supt Nav Malik, of the West Mercia force, made clear the man was not Georgia's boyfriend and they were just "friends on social media".
He said police were investigating a tweet supposedly sent by Georgia, a former head girl and pupil at Ercall Wood Technology College, in the days before she went missing in which she referred to feeling anxious and unable to sleep.
Mr Malik added police were talking to her two sisters about the tweet's significance.
He also confirmed Georgia's father is a detective constable for the force, based in Telford.
Her parents believed she had been expecting to stay overnight with some friends but she never returned. They reported her missing on Tuesday, Mr Malik said.
"We do feel she might've come to harm, given the unique and very unusual circumstances," he said.
Making a direct appeal to Georgia, who has never gone missing before, he said she was not in trouble and urged her to contact police or her parents.
"We are extremely concerned and want to make sure you are safe and well," he said.
She missed her first driving lesson a few days ago and had also been due to go to a concert nearby with her boyfriend but missed that too.
Mr Malik said officers believed that Georgia, who currently attends New College in King Street, Wellington, may have been travelling with a man since she left her home on Sunday.
He appealed to anyone with information about the movements of a silver Toyota Hiace 300 GS van, registration number CX06 ASV, which had travelled from Wellington to Oswestry, Shropshire, before going to Rhyl, Chester, Cumbria and then on to Glasgow.
He also confirmed the van was in the process of being forensically examined.