Compile OpenMP programs with gcc compiler on OS X Yosemite

$ gcc 12.c -fopenmp
12.c:9:9: fatal error: 'omp.h' file not found
#include<omp.h>
    ^
1 error generated.

While compiling openMP programs I get the above error. I am using OS X Yosemite. I first tried by installing native gcc compiler by typing gcc in terminal and later downloaded Xcode too still I got the same error. Then I downloaded gcc through:

$ brew install gcc

Still I'm getting the same error. I did try changing the compiler path too still it shows:

$ which gcc
/usr/bin/gcc

So how do I compile programs with gcc?