However, the blow hasn't ruined their view of the country that has been home for a year, he said.
"We've had an awesome time and it's an amazing place.
"It hasn't tainted our view of New Zealand because since it's happened we've met some people who have been incredible to us."
With only a few weeks left of their year-long stay, the couple were exploring the North Island last week when they stopped at Huka Falls Spa Park carpark about 2pm and decided to go for a swim in the Waikato River.
Deciding it was safer to keep their valuables locked in the van, they took only a small bag and their towels with them.
When they returned an hour later the van was gone.
"Everything was missing. It was just unbelievable," said Mr Horner.
Clad in only their swimsuits, the couple borrowed a phone off nearby tourists and called the police.
Since the theft, the community has extended "incredible" generosity, said Mr Horner.
A Taupo policeman and his wife have taken the couple in, giving them food and a place to stay, Victim Support have helped with clothing and the couple have managed to go bungy jumping and jetboating for free thanks to local generosity.
They have since been able to get access to their bank accounts online and plan to continue their trip around the North Island, before flying out of Auckland on March 21.
Since the theft, a witness reported seeing the couple's red and white van on the Taupo East Arterial Route bypass heading south about 3pm on the day it was taken. There have been no other leads, said Taupo police.
The van's registration is DDS478.
Anyone with information is asked to contact Taupo police on (07) 378 6060.