Denise Preston, 44, from Barlby, Selby, was last seen on Wiggington Road, York at around 9.20pm on Tuesday 7 January 2014.
She is described as white, 5ft 6in tall, with a very slim build and shoulder length blonde hair. When Denise was last seen she was wearing a black body warmer and green jacket, black jeans and black and grey boots.
Although Denise’s whereabouts are unknown it is believed that she is still in York.
Inspector Charlotte Bloxham, of York Safer Neighbourhood Team, said: Denise, if you see or hear this appeal, please get in touch with your sister. She is very concerned about your welfare and wants to know that you are safe and well. If you would prefer to speak to the police, you can contact me and I will reassure your sister that you are okay.
I am also keen to speak to anyone who has seen Denise since the last sighting of her, and urge them to get in touch straight away.
If you can help to locate Denise Preston please contact North Yorkshire Police on 101, select option 1 and pass the information to the Force Control Room.