Why doesn't my GPU work for my mac? Mac info:

iMac (27-inch, Late 2013)

3.2 GHz Intel Core i5

8 GB 1600 MHz DDR3 

NVIDIA GeForce GT 755M 1024 MB



Every time I try to render using my GPU, it crashes, hopefully some of you can give me some good advice, also I've tried going to Nvidia website but they don't have my graphic info so I can't get CUDA (NVIDIA GeForce GT 755M 1024 MB). Is there any other way I can get my GPU to work?

Thank you guys.
Please make sure you have installed the CUDA driver for your mac:
http://www.nvidia.com/object/mac-driver-archive.html

I have a 750M in my MacBook Pro (2.8 GHz Intel Core i7) and it renders about as fast as the CPU as long as the render job's RAM requirement doesn't exceed the RAM on the video card. In fact, I often render overnight with both CPU and GPU concurrently as separate command lines.