Eloise Worledge was just eight years old when she went missing on January 13, 1976, and police say thousands of searches and interviews have done little to track her down.
On the 50th anniversary of her disappearance from her family home in Beaumaris, in Melbourne's southeast, a $1 million reward for relevant information has been announced.
The reward is for information that either helps identify who was behind her disappearance, or for helping police locate her body.
The disappearance has always been treated as suspicious and police believe Eloise was murdered.
Eloise's surviving family members said their lives had been changed since she disappeared.
"(Our) memories of waking up to find her missing are still very vivid and raw and the passage of time has not eased the pain of this loss," a family statement read.
"Ella was and remains deeply loved, she was more than a missing person or a case file - she was a daughter, a sister, a friend, someone who mattered greatly to all who knew her."
Eloise's parents found the flyscreen on her window cut open when they looked for her in the morning, having last been at 11.40pm the night before.
Describing her as quiet and intelligent, the parents said she would not have left home voluntarily.
At the time, 250 police searched the area for nearly three weeks and canvassed 6000 properties, but no sign of Eloise was found.
Homicide detectives reviewed the case in the early 2000s, conducting new forensic testing and re-interviewing persons of interest, but did not find anything substantial.
A coronial inquest in 2003 culminated with an open finding, meaning the coroner did not think it possible to find anyone responsible for the death on the evidence available.
Eloise's mother alleged at the time of the disappearance her husband could have been involved, but the lead detective involved in the case told the inquest he found no evidence to implicate either of Eloise's parents, Lindsay and Patsy Worledge.
Both have since died.
"The ongoing public interest and constant suspicion surrounding (our) family – found to be unsubstantiated more than once – caused a lifetime of immense grief and pain," the family said.
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