The hashtag plugin for Joomla! is executed in all components that supports content plugins, including Joomla! articles and K2 Items. It searches for #anything and replaces it with a link over the hashtag that goes directly to either the search component or to the smart search (finder) component.
When you write an article just type # to any word and will be converted to link automagically!
When clicking on tag #anything, results will display all articles that contain "anything" and not only the ones with the hashtag in it.
The plugin has two parameters: to use either com_search or com_finder and to select Menu Item from one of both components - com_search or com_finder if they are already created in your site.