Gerard disappeared while walking along Kent Street in Rockingham on his way to a comic store with his brother, who had skated ahead on his rollerblades, on October 14, 1997.

His body was found dumped in a pine plantation, about 20km southeast of Rockingham, two weeks later.

Police Minister Michelle Roberts on Wednesday announced a reward of up to $1 million for information leading to his killer's apprehension and conviction.

"Today Gerard should be a young man, perhaps with a family of his own," she said on the 23rd anniversary of his disappearance.

"He was robbed of that future and his parents were robbed of that future.

"I hope that with this added incentive, we can come closer to resolving the murder. I know that our police will never give up on pursuing justice for Gerard."

In a statement, the Ross family said it was grateful to the government for the substantially increased reward.

"As we head into another year without him, we are sadly reminded that someone somewhere knows what happened to our beautiful funny and loving boy," the family said.

"From Gerard's family and friends on both sides of the world, and the community of Western Australia, please come forward and take this opportunity to provide justice for Gerard."

Ms Roberts said anyone who came forward with information leading to the killer's conviction may be considered for a pardon or protection from prosecution.

WA Police last year said all evidence linked to the abduction and murder was being re-investigated as part of a fresh cold case review.

Australian Associated Press