Question: I installed rustup with brew command but still says that rustup command is not found. I am not sure if I am missing any installation step. Any help would be appreciated.

Answer: 
Did you try to install rustup via <https://rustup.rs/>

That may work correctly on your computer.
I had the same problem, because the PATH variable didn't include the Cargo's bin directory right after installation.

I closed and opened again the shell, and it worked!