Zoe Zaremba, from Aiskew in North Yorkshire, was last seen at her home on Saturday, June 13.
North Yorkshire Police say they are 'extremely concerned' for her welfare and have carried out extensive searches to find her.
The police helicopter and the police dog units have been involved in the searches, as well as help from local volunteers.
The appeal to find her is being supported by the Missing People charity and a poster to help find Zoe is now available to download from their website.
Earlier this week, Zoe’s mother, Jean Zaremba, appealed directly to her: “Zoe, we are so worried about you, your friends, the local community, everyone is worried sick and everyone cares about you.
"We just want you back home safe. We love you so much. Please come home or let us know where you are.”
Zoe, who has autism, is described as around five foot six inches tall, of slim build with brown eyes and brown hair which she usually wears in a ponytail.
She is believed to have been wearing a blue ‘keep calm’ t-shirt, purple jogging bottoms, white and purple Lonsdale trainers and a silver heart shape necklace with an orange crystal.
People in the Aiskew area are asked to double-check CCTV and dash-cam footage for any potential sightings, as well as gardens and outbuildings.
If you think you might have seen Zoe, or have any information about her current whereabouts, please contact North Yorkshire Police on 101 and pass information to the Force Control Room.
If you have an immediate sighting of her, please call 999.
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