Nyika said he was taking the medal to show a young fan at a school in the city when he realised thieves had snatched it from his vehicle.
"At first I was quite embarrassed about it, but now I'm just angry," the 22-year-old told TVNZ.
"I just want the medal back. It's almost worthless to anyone but me, you know, so I really hope I can get it back."
Detective Sergeant Paul Slater said police were reviewing CCTV footage from locations around Auckland to catch the culprits.
"Obviously a Commonwealth Games medal is very distinctive and of high sentimental value to the victim and his family," he said.
"Our priority is to return this medal to its rightful owner."
Nyika won light-heavyweight gold at the Glasgow Commonwealth Games in 2014, then followed up with gold in the heavyweight division this year on Australia's Gold Coast.
After the win he spoke about joining fellow Kiwi heavyweight Joseph Parker in the professional ranks.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)