His partner noticed he was in trouble and tried to raise the alarm.
It's understood he disappeared beneath the surface very quickly, and was not seen again.
An extensive air, land and water search was launched - which included helicopters from Taranaki and Whanganui, a Coast Guard vessel, a police search and rescue team, volunteers from the community and members of the teenager's family.
Whanganui mayor Annette Main has said in recent days that the tragedy will affect the close-knit community hard.
"It'll be somebody that we all know, either personally or who we know of," she said.
"It's a lovely beach, everybody loves going out there on Christmas afternoon and to lose somebody like that is really tragic, especially on Christmas Day."
Whanganui Inspector Gini Welch yesterday said the incident highlighted the dangers of rips and currents, especially on west coast beaches.
"Everyone is celebrating and relaxing, and it's just a reminder to all of us that it's not just our homes, schools, and roads that we need to keep safe," she said.
"We need to keep ourselves and our families safe in the water as well."
