Jessica Wallwork was last seen at approximately 8-45pm on Sunday (August 28th) when she left an address in Railway Street in the town.
She has not made contact with friends or family since then, and is not answering her phone.
Anybody who has seen her, or has information about where she might be, is urged to contact police immediately.
Police have today issued two new photos of Jessica in the hope that somebody will recognise her or has seen her.
PC Fiona Hall, of Nelson Police, said: “Both we and Jessica’s family are extremely concerned about her and we would ask anybody who knows where she might be to get in touch.
“Similarly we would urge Jessica, if she sees this appeal, to get in touch and let us know she is safe.”
Jessica is described as white with shoulder-length, light brown hair. She was last seen wearing a blue hooded top with "LEC" on the front, light blue skinny jeans and a cream-coloured handbag. It’s possible she was wearing trainers.
Anybody with information should contact police on 101, quoting log number 955 of August 29th.