Can't create virtualenv
If you want to use a command without typing the path to the executable, you need to put it (or a symbolic link to it) in one of the the directories where the system looks for executable whenever no path to the command is provided, for example /usr/bin and /usr/local/bin.

So in your case I would put a symbolic link to virtualenv in /usr/local/bin:

ln -s /path/to/virtualenv /usr/local/bin/virtualenv