The search extension for Google Plus is available now!
Currently, Google doesn't support for searching Google Plus directly, you must add site:plus.google.com to the end of the query string in Google search box.
I just developed a small Chrome extension to search Google Plus, you can free install it. This extension enables you to search the Google Plus public contents online by one click, it can filter the profiles, pots, posts from Buzz and posts from Google Reader.
To install this extension, just visit Chrome web store, and then click the Install button.