Disable Search Plugin disable’s the search capabilities of WordPress.
Prevent WordPress from allowing and servicing any search requests for the blog.
* Prevents the search form from appearing (if the theme uses the standard get_search_form() function to display the search form).
* Prevents the Search widget from displaying the search form.
* With or without the search form, the plugin prevents any direct or manual requests by visitors, via either GET or POST requests, from actually returning any search results.
* Submitted attempts at a search will be given a 404 File Not Found response, rendered by your sites 404.php template, if present.
Find out more at: http://wordpress.org/extend/plugins/disable-search/