Police believe Mr Piper, from Paekakariki, has been murdered, but his body has not been located.
Armed police swooped on a State Highway 1 layby near Otaki yesterday to help arrest the 51-year-old man.
Detective Senior Sergeant Mike Oxnam said the man was taken into custody after being arrested just south of Otaki bridge and would appear in Porirua District Court today.
Mr Oxnam told reporters that the armed offenders squad helped arrest the man, who had been driving north on SH1 and co-operated when confronted by police.
Mr Piper, 23, was last seen on May 15 when he disappeared from the home of his former partner, Hanna Lark, in Eatwell Avenue, Paraparaumu.
Mr Oxnam said the police were appealing for public sightings of three vehicles, including a grey 1988 Toyota Corolla saloon which may have travelled as far as Wanganui on the weekend of May 15-16, when Mr Piper went missing. The man was arrested yesterday was from that car.
But Mr Oxnam said the "key" vehicle in the investigation was a dark green Mazda Marvie 4WD, registration number WC9996, that police seized in Turakina, south of Wanganui, on June 8.
"We know that Raymond was in the 4WD on Saturday, May 15, and then that vehicle has gone to Turakina," he said.
"Once we recovered that vehicle and carried out a forensic examination we were able to say this was no longer a missing person's inquiry, it was a homicide inquiry. But I can't go into the reasons for that."
The Toyota Corolla or a red to maroon-coloured 1993 Nissan Bluebird, registration number RZ2075, seized on June 16, may have been used by "a person or persons" to drive away from Turakina, Mr Oxnam said.
Mr Oxnam said the main focus of the police inquiry was to find Mr Piper's body and return it to his family.
"I am actually quite pleased we have made this progress, but the important thing is to get their Son back to them," he said.
In a statement, the family said they could not rest until Son was brought home.
