Try:
supervisorctl reread
supervisorctl reload
That should start the service. I did this as root under Ubuntu 13.04.
EDIT:
I've had trouble since I posted this with SIGHUP'ing Supervisor processes. I would just like to share a little snippet I found elsewhere:
sudo kill -HUP `sudo supervisorctl status | grep $APP_NAME | sed -n '/RUNNING/s/.*pid \([[:digit:]]\+\).*/\1/p'`
The below will send a SIGHUP to the process running APP_NAME. This is useful for Gunicorn graceful reloading.
Joe