Margaret Fleming, 36, was reported missing by her two carers from her home in Main Road, Inverkip, Inverclyde, seven weeks ago, but the last independent sighting of her was actually at a family event on December 17 1999.
Officers have said it is possible Ms Fleming, who is believed to have learning difficulties, “may have come to some harm’’ and say their priority is establishing her movements and lifestyle from 1999 onwards.
Specialist search teams have been combing the cottage where she lived and excavating its grounds in recent days with a view to finding any documents, clothes or other personal items that could help in the effort to track her down.
Police have already had a good response to previous pleas for information but they still want to hear from more people.
Detective Chief Inspector Paul Livingstone, the senior investigating officer, said: “Today, Saturday December 17, marks 17 years to the day that Margaret was seen at a family gathering.
“This is the only independent sighting we have of Margaret so far and I would like to re-appeal to people in the local community of Inverkip and beyond for their help with our enquiries.
“A priority for the inquiry team is to establish Margaret’s movements and lifestyle between 1999 and when she was reported missing on Friday October 28 by her carers.
“We have had an encouraging response to our previous appeals and I would like to thank everyone who has taken the time to come forward with information.”
In an appeal to the missing woman, Mr Livingstone added: “If Margaret is reading this, I would ask her to get in touch with police. She is not is any trouble, we just want to ensure she is safe and well.”
It is understood police went to the house as part of a routine social services enquiry in October but were told she was not there, and her carers later reported her missing.
The missing woman is said to have few contactable friends or family and checks on education, employment, health and welfare records have shown no trace of her.
Police are making inquiries in the wider Inverclyde area as part of their investigation.
Ms Fleming is believed to have attended James Watt College in Greenock between 1996 and 1998.
She is thought to have lived with her father in Port Glasgow before he died in October 1995.
She then lived with her grandparents and her mother, but later moved in with carers in 1997 and has been estranged from her mother since.
Ms Fleming is described as 5ft 5ins with a heavy build, collar-length black hair and brown eyes.
When reported missing on October 28, she was wearing a green tartan fleece or jumper, dark-coloured jeans or trousers, dark Karrimor boots and was carrying a satchel-type handbag.
Anyone with information is asked to contact police on 101.