Advanced Search for K2 items is a Joomla! plugin which allows you to search for text, tags or attachments in K2 items. This plugin takes your choice into the search component, i.e. it respects if you are looking for "any word", "all words" or "exact phrase", something that does not occur in the standard plugin.
The plugin also comes with words and without accents. Allows configuration of whether or not search for "tag" and "attachments".
I did this based on the original K2 plugin, due to a need in my work, to improve the user experience and it's available to everyone for free.