Make sure you've read over the FAQ before sending support mail or making forum posts. I try to update it often enough with common questions.
When asking for help configuring Prowl (your notifications don't show up, etc.) please include screenshots of your Prowl style in Growl.
Twitter
Follow @prowlapp
Email
Email prowl-support@googlegroups.com for support.
Forums
Post on the Prowl forums for support or feedback.