Colleen Jarvis, 55, was last seen leaving her home in Burlington Avenue, York at around 12.15pm on Thursday May 26.
Police believe she could have travelled outside of York and particularly likes visiting Knaresborough, Harrogate and Malton.
Her family have released a new photograph of Ms Jarvis in a bid to jog the memory of members of the public.
In a statement they said: “Please Colleen – we are so worried about you. You’re not in any trouble. Just let us know you’re ok. We love you and miss you.”
Meanwhile, North Yorkshire Police said they are increasingly concerned for her welfare.
Inspector Carol Kirk, of North Yorkshire Police, said: “Four days have passed since Colleen was last seen.
“We’re continuing to work around the clock to try to find her but we need the public’s help.
“If you think you may have seen Colleen or any information, no matter how small, I’d urge you to contact us immediately.”
Ms Jarvis regularly travels by public transport, and police are urging anyone who uses buses or trains to be on the lookout for her.
Anyone with any information is asked to contact North Yorkshire Police on 101.