A police spokesman said Maritime New Zealand would broadcast regular reminders to boaties in the area to keep on the lookout for the teen, and local surf lifesaving clubs were all aware of the missing boy.
The teen was swimming on Christmas Day about 3pm beside his girlfriend and close to the surf club at the popular beach, when he was caught in a rip.
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.
However, after having found no sign of the teen by about 9.30pm, the effort was suspended and re-launched at first light yesterday.
But a Castlecliff Surf Club spokesman said lifeguards with a boat in the water "had no luck" finding the boy, though conditions were calm and clear, and the surf was flat.
Whanganui Inspector Gini Welch yesterday said police had "searched everywhere we can".
"It's a very tragic accident. Getting caught in a rip is the most awful and unfortunate thing to happen to anybody [in the surf]."
Wanganui mayor Annette Main said the tragedy would 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."
It highlighted the dangers of rips and currents, especially on West Coach beaches, Ms Welch said.
"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."
There are fears that as many as five people have now drowned around New Zealand's coastline since Christmas Day.
An 82-year-old drowned in a pond at Opito Bay near Kerikeri yesterday morning.
And on Christmas Day three people -- including a 3-year-old boy -- died in a string of water tragedies.
