Uninstall virtualenv, Mac
I encountered the same problem. I solved it by creating an empty file called RECORD in the virtualenv directory. 

On my machine, the command to run in Terminal was 

 touch /usr/local/lib/python2.7/site-packages/virtualenv-1.11.6.dist-info/RECORD


That's it. After doing that, pip install virtualenv --upgrade worked for me.