Claire Middlehurst, from St Helens, has been missing for over a month, police said.
The 36 year old was last seen in Newton-Le-Willows on Sunday, July 21, but officers now suspect that she could be in the Blackpool area.
She is 5'11 and slim, with blonde hair, though police believe she changes her hair colour often.
Officers think Claire could be with a man of a similar age to her.
PC Ken Armstrong said: “It’s been over a month since Claire was last seen and we are concerned for her welfare. If you have seen Claire or a woman matching her description, please get in touch with us.
“Claire – if you are reading this, please call us and let us know you are okay.”
Anyone with information should call 101 quoting log number 989 of 20th August.