network wide search solution

If you are looking to have a complete search, Adam (wpmodder) has done an excellent writeup here:

https://wpmodder.com/how-to-use-thematic-and-the-wpsearchmu-plugin-to-display-sitewide-search-results-860.html

Now, some of it is specific to his theme, but your theme should be easy enough to mod. Also note the updated search plugin.