Detectives from the Metropolitan Police's East Area Missing Persons Unit are appealing for information regarding the disappearance of Suzanne Lawrence, who went missing in the summer of 1979.
Suzanne, then 14, left her home in Harold Hill, east London, on 27 July 1979 with her then 13-year-old sister, Michelle. The sisters had told their mother they would be staying with friends in Dagenham.
Michelle returned home on 31 July after an argument with Suzanne. She told police they had met three teenage boys at a fair in Highbury Fields, north London, who took them to a nearby squat. Michelle was unable to locate the squat when she visited the area with police.
At the time, officers thought Suzanne may have joined a travelling fair, but inquiries did not locate her. The case was not closed, and detectives are now appealing for any information that could help establish what happened to her.
Michelle, now known as Hooper, said: "If my sister is alive, I want her to know that she has never been forgotten." She added that her mother is now elderly and has lived for decades without knowing what became of her daughter.
Det Ch Insp Kam Sodhi, leading the investigation, appealed for information on the three teenage boys, believed to be aged between 14 and 17, who took the sisters to the squat. The force is keeping an open mind over the circumstances of Suzanne's disappearance, including whether she may have come to harm.
Suzanne would now be 61, and detectives have released two e-fit images showing how she may look now. She was described as a white girl, about 5'3" to 5'5" in height, of slim build, with dark brown straight hair, and spoke with a local, Essex accent.