[support] $block['content'].= drupal_get_form('search_form', NULL, $keys, 'event'); problem

Hi Friends $block['content'].= drupal_get_form('search_form', NULL, $keys, 'event'); i have used this code in my custom block, I got the search box, But it is not searched anything, drupal_get_form('search_form', NULL, $keys, 'event'); for this function, i have to supply any value ??? Any idea