Sarah Everard, 33, has been missing since leaving her friend's home near Clapham Common on Wednesday 3 March at 9pm.
The Marketing Executive, from South London, should have arrived back at her home in Brixton around 50 minutes later, after walking through Clapham Common.
But police are unsure if Sarah ever made it home. She was last spotted on CCTV at approximately 9.30pm, walking alone, in the direction of Tulse Hill.
Now, six days on, Sarah hasn't been seen or heard from since.
Police have widened the search and the case is being led by Scotland Yard’s Specialist Crime Command, which deals with homicides and major crime, because of the 'complex nature' of the case.
However, the force insists it is still very much a missing persons inquiry and they're calling for witnesses to come forward with any information or sightings.
Sarah is described as 5’4 tall, with blonde hair and of a slim build. She was last seen wearing turquoise and orange trainers, navy blue trousers with a white diamond pattern, a green jacket, green earphones and a white beanie hat.
In a statement, Sarah's family said, "With every day that goes by we are getting more worried about Sarah. She is always in regular contact with us and with her friends and it is totally out of character for her to disappear like this. We long to see her and want nothing more than for her to be found safe and well.
"We are so grateful to the police and all our friends for all they are doing.
"We are desperate for news and if anyone knows anything about what has happened to her, we would urge you to please come forward and speak to the police. No piece of information is too insignificant."
Sarah's uncle, Nick Everard, told The Sun, "If someone is holding her against her will I would plead with them just to be human and to let her come home, to let her talk to us, give us a ring or text to let us know she is OK."
He added, “These are desperate times for the family. We know the police are doing everything they can but it’s the not knowing what has happened after four days is agonising”.
On Twitter, Lambeth Police force revealed they're 'increasingly concerned' for the Sarah, after her disappearance.
No piece of information is insignificant. If you've seen Sarah, or if you have any information, please call the Met Police incident room on 0208 785 8244 to speak to an officer, or leave information here
Information can also be provided anonymously by calling the Missing People charity on 116 000 or 116000@missingpeople.org.uk