Eleven-year-old Gerard Ross was snatched off a street in Rockingham, Western Australia, in October 1997. His body was discovered two weeks later.
His grief-stricken family later moved to Queensland, before returning back home to Scotland.
Yesterday, his mother Cyrese and father Stewart urged anyone with information about the murder to come forward.
Ms Ross, from Burntisland, Fife, said: "It's 15 years ago today since we last saw Gerard.
"We miss his love, his humour and feel an overwhelming loss of his presence within our family.
"On behalf of Gerard and our whole family we would like to put out an appeal to anyone who knows the person or person involved with Gerard's abduction and murder to please come forward and give this information to the police."
The Ross family were holidaying in the seaside town of Rockingham when Gerard was grabbed as he walked to a nearby comic shop.
His 13-year-old brother Malcolm had set off with him, but was wearing roller-blades and had gone ahead.
The youngster was only 800m from the family holiday home when he vanished.
His body was found 15 days later at a pine plantation in Karnup, 12 miles from where he disappeared.
Detectives at the time said Gerard had suffered a "brutal death for no reason". His body was fully clothed and appeared to have been hurriedly dumped.
Police have confirmed that a £63,000 reward announced on the first anniversary of Gerard's abduction still stands.
The Ross family put together a book of Gerard's crayon drawings to raise funds and warn children to stay away from strangers.