"This is a horrifying case in which terrible pain and suffering - and permanent disability - has been inflicted on an animal," SPCA Auckland executive director Bob Kerridge said.
"It is illegal for so-called 'leg-hold traps' to be used within 150 metres of a dwelling without the express permission of the occupier or in any area where there is a probable risk of catching a pet. There is no way both of these conditions could be met in suburban Henderson."
The cat's owner was probably looking for him now.
"If anyone recognises this cat or has any information that might help us to reunite it with its owner, we desperately want to hear from them. We also want any information that might help us track down whoever set this trap so we can take them to court," Mr Kerridge said.
Anyone with information should call Auckland SPCA on (09) 256 7300.
The Government restricted the sale and use of gin traps in 2008.