Image copyright NSW Police

Police have announced a breakthrough in the investigation into a British-born toddler who was kidnapped on an Australian beach 46 years ago.

Three-year-old Cheryl Grimmer was abducted in 1970 and has never been found.

Now, almost 50 years later, detectives believe new information has led them to identify a suspect.

Cheryl's brother appealed for "something so we can mourn" as the new search was launched.

Cheryl Grimmer disappeared on 12 January 1970 in the Illawarra district, New South Wales.

The toddler had been at Fairy Meadow Beach with her mother and three brothers.

The family were living nearby, having recently emigrated from England.

Cheryl was sent to the shower block with her brothers. It was from these changing rooms that detectives believe she was taken.

Image copyright NSW Police Image caption Cheryl with her late father, Vince Grimmer

Image copyright NSW Police Image caption Fairy Meadow surf club in the 1970s

Detectives recently returned to Fairy Meadow Beach with several key witnesses in a bid to draw further on their memories.

Now in their 50s, those witnesses were aged nine, 10 and 12 at the time.

The latest investigation is focusing on a male youth seen in the immediate vicinity of the surf club pavilion in the morning and afternoon of the day Cheryl was taken.

At the time, it is thought, he was aged between 16 and 17, and so he would now be in his early 60s.

The young man was described as being white, about 152cm or five feet tall, of medium build, with brown hair, blue eyes and a fair complexion.

Image copyright NSW Police Image caption Cheryl's brother, Stephen Grimmer, returned to Fairy Meadow Beach with witnesses

The Wollongong local area command crime manager, Det Insp Brad Ainsworth, said Cheryl's disappearance was a mystery the police still desperately wanted to solve.

"Cheryl's kidnapping sparked a massive manhunt and stunned the Illawarra," he said.

"The witnesses' return to the beach has yielded promising results, and we hope someone in the community may be able to help us identify this male youth."

Heartache

It was not until May 2011 that a coroner concluded Cheryl had died sometime after her disappearance, the cause being unknown.

In 2012 the New South Wales government offered a $100,000 reward for any new information.

Cheryl's parents died without knowing what had happened to their daughter. But speaking to the Illawarra Mercury in 2011, Carole Grimmer said she believed her daughter was still alive.

Cheryl's three brothers - Ricki, Paul and Stephen Grimmer - were at a press conference outside the Fairy Meadow Surf Club on Monday.

Ricki Grimmer was tearful as he stood before reporters.

He said: "It's heartache. Decisions I made on the day were wrong. I shouldn't have left. Everybody says 'It wasn't your fault.' Come and stand where I'm standing; see what it feels like.

"Just let us know where she is, give us something so we can mourn."

Stephen Grimmer, now 52, said: " My mum and dad have passed on now not knowing, and we want to know too before we pass on."

Det Insp Ainsworth added: "We would dearly love to provide answers to Steve and his family, solve this matter for the people of the Illawarra, and ultimately provide Cheryl with some dignity in death."