Indian student Srikanth Rayadurgam, 23, has been missing since October 1.
Fears for his safety have been growing since some of his personal items were found near Auckland's Westhaven Marina the following day.
Today his brother-in-law Nagesh Kakanoor said he was prepared for the worst but the family desperately wanted Mr Rayadurgam home, dead or alive.
He said he had found the name badge from the Pizza Hutt where the missing man worked part time, and his scarf.
Both were in the water near the marina and near where his other items were found.
"I am strongly thinking there could be some foul play - big time," Mr Kakanoor said.
Mr Rayadurgam's disappearance was completely out of character, he said.
He had been in New Zealand since February and was living with Mr Kakanoor and his wife Padam.
They were a close family and without him the house was very different.
"We used to have so much fun.
"I am prepared for the worst. My family is shattered. We want him (back) dead or alive. We don't know what direction we have been going in for the last 12 days."
Mr Kakanoor said every day since Mr Rayadurgam had disappeared he had been down at the harbour looking for clues.
"I am seeking public help," he said.
Yesterday the mystery deepened when police said he had not been at some of Auckland University of Technology classes since August 17.
However, Mr Kakanoor said some of that was holidays and some of the classes were not important , so his brother-in-law had stayed at home to study.
There was no sinister reason for him not attending classes.
The day he disappeared he took $250 from a money machine, which police said was a large amount of cash for him to have.
Police also said his mobile phone was detected in Karangahape Rd late on Thursday night and early on Friday morning.
Mr Kakanoor said his brother-in-law did not go out clubbing and would not have been involved with sex workers.
