The Joomla extension K2 AJAX Search allows you to search contents of the K2 component and makes it possible to filter by multiple categories, by multi-select list extra fields and by creation date. The extension has a beautiful appearance, shows a list of previous results by using AJAX and is highly customizable.

Joomla 3.x compatibleJoomla 2.5 compatible

 

The extension is no longer actively maintained so use at your own risk. Any contribution is welcome.