The young people were out hunting virtual cartoon characters in the North Island town of Napier on Wednesday night, when they heard a car alarm and saw a masked man run past, New Zealand Police said.
"They didn't use Pokeballs to catch him, they just held him till police arrived," police said in a statement, referring to an online tool used to capture the Pokemons that appear in places such as temples and landmarks where people gather.
A 28-year-old man was arrested and will face theft charges in court on September 7, police said.
Nintendo's Pokemon Go has become an unexpected smash hit, using augmented reality and Google mapping to make animated characters appear in the real world, overlaid on the nearby landscape viewed through players' mobile phone cameras.
The game has also been blamed for injuries and robberies of distracted users in some countries, prompting authorities to warn gamers to play responsibly.
In Napier, police reminded players their own safety was paramount.
"Capturing little Pokemon monsters isn't just good for the players because in this case it's good for the police too, but we don't want any good Samaritans to get hurt," said Senior Sergeant David Sutherland.