HOW TO: Add Search to Google Reader
Search is one of the most requested features for Google Reader. Until this feature is implemented, there’s a simple workaround: you 
can use Google Co-op to create a search engine restricted only to the sites you’re subscribed to. Here’s how to do this:
1. Go to this page that shows your list of subscriptions (in OPML format) and save it to your desktop. Google Operating System: How to Add Search to Google Reader