Lynda Spence has not been seen since April 13 when she left her mum's home in Glasgow Harbour.
She sent a text to her mum the next day saying she had gone to London, but her parents reported her missing a few weeks later.
Police today made a new appeal on her 28th birthday.
Detective Superintendent Alan Buchanan said: "Patricia and James are still suffering the anguish of not knowing what has happened to their daughter.
"People with information on Lynda should examine their conscience and pass on any information or details to us."
He added that police believe she has "come to harm".
Ms Spence is also known as Lynda Zefaj, Lynda Palmer and Lynda Reilly.
Anyone with information should call 0141 532 3270 or Crimestoppers on 0800 555 111, text 07864 178454, or e-mail lynda email@example.com