No module named flask using virtualenv

Question

I am following these steps to learn flask http://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-i-hello-world/page/0#comments

I ran this command to create the virtual env:

python virtualenv.py flask 

When I try to start flask using the python.exe file in my project scripts directory, it says

No module named flask 

My PATH is set to the python directory that virtualenv installed. Why is it not able to find flask?

I initially started with the official Flask quickstart guide and was able to get the webserver to run, but with this virtual env install it is not working.