How to get pip to work behind a proxy server

How to get pip to work behind a proxy server

I am trying to use python package manager pip to install a package and
it's dependencies from the internet. However I am behind a proxy in my
college and have already set the http_proxy environment variable. But when
I try to install a package like this:
pip install TwitterApi
I get this error in the log file:
Getting page http://pypi.python.org/simple/TwitterApi
Could not fetch URL http://pypi.python.org/simple/TwitterApi: <urlopen
error [Errno 111] Connection refused>
Will skip URL http://pypi.python.org/simple/TwitterApi when looking for
download links for TwitterApi
Getting page http://pypi.python.org/simple/
Could not fetch URL http://pypi.python.org/simple/: <urlopen error [Errno
111] Connection refused>
I even tried setting my proxy variable explicitly like this:
pip install --proxy http://user:password@proxyserver:port TwitterApi
But I still get the same error. How do I get pip to work behind a proxy
server.