Denise Dearden was last seen late on Saturday August 19 in Chorley town centre having drinks at the White Hart.
She is described as white, slim build and 5ft 6inches tall, long brown hair and wears glasses.
A spokesman for the police said: "We appeal to anyone who sees Denise or knows where she might be to get in touch with us.
"We also ask Denise her-self to make contact if she sees this appeal to let us know she is safe and well."
Anyone with information should contact police on 101 quoting the log number LC-20170821-1314.