Mr Protheroe is 185cm tall and has a solid build and a distinctive shaved haircut with a rat's tail hanging from the back. He was last seen wearing three-quarter pants, jandals and a dark-coloured shirt.
"There is nothing to indicate that there was anything untoward. It's a big question mark, really, we just don't have any idea where he is," Mr Watson said.
He had a message for Mr Protheroe. "Just please let someone know you're safe, that would be my appeal."
If you can help police find Garrick Protheroe or see the car he was driving, registration CZ539, contact Sergeant Grant Watson on (09) 839-0600.