Layla Mann was last seen at 11.10am on Monday 12 March 2018 at a bus stop on Columbia Road.
She is described as being of medium build and has dark hair which is often worn in a messy bun with the nape of her neck shaved. She was last seen wearing black leggings and a blue Puma hooded top.
Inspector Dougie Bader, of Dorset Police, said: “Although Layla has been in contact with officers via phone and social media since Monday, we need to find Layla and confirm that she is safe and well.
“We are becoming increasingly concerned for Layla and I would urge anyone who has seen her or a girl matching the description given to please contact Dorset Police.
“It is possible that Layla is with someone and, while they may have good intentions for Layla, I would ask them to please make contact with us.
“If Layla sees this appeal – please tell us where you are as we and your family are very worried about you and we just want to see you in person to make sure you are ok.”
Anyone with information or knowledge as to Layla’s whereabouts is asked to contact Dorset Police at www.dorset.police.uk, via email firstname.lastname@example.org or by calling 101, quoting occurrence number 55180037252.