Vim : Can't set up Ctags

Question

I have question about setting up Ctags/Vim.

First, I did

$ brew install ctags

and in my working directory

$ pwd
~/projects/rails/rep

$ ctags -R

then I got tags file in my working directory; rep.

and in my .vimrc file

set tags=tags;/

On the method I want to jump, I did Ctrl + ], but I got

E426: tag not found: method_name

I have no idea which is the reason I cannot use ctags...

Thanks.