Officers say they are “extremely concerned” about the welfare of Katie Kenyon who has not been seen since last week.
It is believed a woman matching Katie’s description left an address in Todmorden Road, Burnley at around 9:30am on Friday with a man.
The pair travelled in the Ford Transit van, registration MT57 FLC, to the Bolton-by-Bowland area. She has not been seen since.
A police spokesperson said: “We want to hear from anyone who recognises this van.
“We remain extremely concerned about Katie’s welfare.
“Detectives from our Force Major investigation Team are following a number of lines of enquiry to try and find out what has happened to her.
“Her family are extremely concerned and say Katie’s disappearance is out of character for her. They are currently being supported by specially trained officers.
“We are continuing to search in the area along with partners from Lancashire Fire and Rescue Service and mountain rescue teams.
“A 50-year-old man from Burnley was arrested on suspicion of kidnap and detectives have today been given a further 36 hours to question him. That man is known to Katie.”
Katie is described as white, 33, f5ft 9ins tall, with shoulder length strawberry blond/ginger hair. She was last seen wearing a blue shirt/jacket and white top, black leggings and flip flops.
DCI Al Davies, of the Force Major Investigation Team, said: “We continue to be extremely concerned about Katie and we have a large team who are working hard to try and find out what has happened to her.
“I am keeping an open mind about what has happened to her, but my concern obviously grows as time goes by.
“I would appeal again to anyone who was in the Bolton-by-Bowland area on Friday and saw anything suspicious to get in touch, especially if they saw the silver van or Katie alone or in company.
"Please do come and speak to us even if you think the information you have may not be important.”
Anyone with information should call police on 101 quoting log 800 of April 24th or contact us through the Major Incident Public Portal at https://mipp.police.uk/operation/0401020119P01-PO1
Alternatively contact independent charity Crimestoppers on 0800 555 111.