Several new persons of interest have been identified in the unsolved murder of an 11-year-old schoolboy in Perth, police say.

Key points: Gerard Ross was abducted and killed in 1997 while holidaying in Perth with his family

Gerard Ross was abducted and killed in 1997 while holidaying in Perth with his family Police say they have new 'persons of interest' following a cold case review

Police say they have new 'persons of interest' following a cold case review Police want to speak with man who approached another young boy on the same road before the abduction

Gerard Ross was abducted while on a family holiday in Rockingham in 1997.

His body was found dumped in a pine plantation near Baldivis and Stakehill roads 20 kilometres away, 14 days later after several unconfirmed sightings.

WA Police have made a fresh appeal to the public to help find his killer following a cold-case review which began in 2014.

Since then the Special Crime Squad has been working through the review recommendations and opened up new lines of inquiry which police hope will lead to a breakthrough, Acting Detective Inspector Jon Munday said.

"This was a crime that shocked all West Australians," Acting Inspector Munday said.

Acting Detective Inspector Jon Munday has called for public help. ( ABC News: Charlotte Hamlyn )

"Despite the passage of time the WA Police remain committed to resolving this matter and bringing the killer or killers to justice, as well as providing some closure for the Ross family."

Police say several new persons of interest have been identified, but would not give any information about who they were or their possible links to the case.

"We believe there are still people in the community who know what happened to Gerard," Acting Inspector Munday said.

"I would ask them that, given the passage of time or changes in circumstances or allegiances, [they] please reconsider and come forward.

"Ask yourself 'what if it was my child or what if it was my grandchild'."

Driver asked to come forward

Police have released an image of a hat worn by Gerard, that was never recovered from the scene, which they hope may have been spotted by the public, or jog someone's memory.

The hat that was never recovered in the Gerard Ross abduction and murder cold case. ( Supplied: WA Police )

They are also trying to identify the driver of a beige or cream sedan that reportedly approached a young boy waiting at a Kent Street bus stop near the Rockingham public library a few weeks before Gerard disappeared.

"We don't have a precise date, but in August 1997 a male driver pulled over at the bus stop and asked the 11-year-old if he wanted a lift," Acting Inspector Munday said.

"When the boy declined, the man drove away."

"The vehicle and its driver have never been identified due to the vague description provided but we are still keen to speak to that person, if only to eliminate him from the investigation."

WA Police say they have collected more than 5,000 pieces of physical evidence in the long-running investigation and have spoken to almost 1,200 witnesses.

In 1998, the WA Government offered a $100,000 reward for information about Gerard's murder, and that offer still remains in place, according to police.

Police also ruled out any link to the death of Queensland teenager Daniel Morcombe who disappeared in similar circumstances on the Sunshine Coast in 2003.

Brett Peter Cowan, who was born in Western Australia, was convicted of that murder after an eight-year investigation. Police said Cowan was in custody in Queensland at the time of Gerard's murder.

'He will never experience the joy in sharing his love'

Gerard Ross would have turned 31 this year, his mother said. ( Supplied )

Gerard's mother Cyrese, who now lives in Scotland, released a statement.

"Gerard would have turned 31 last November and has sadly missed out on so much life," she said.

"He will never experience the joy in sharing his love, creative talent and sense of humour with his niece or when starting his own family.

"We make this appeal on behalf of Gerard, and ask you to provide any information, no matter how small or insignificant.

"Please come forward as it can make the difference to Gerard's life and give him the justice he deserves."