Wordpress 3.6 Searchform.php isn't seen anymore. Add this to your functions.

functions.php

// Wordpress 3.6 seems to have messed up the searchform
// Credit: http://salferrarello.com/searchform-php-wordpress-3-6-broken/
function search_form_no_filters() {
  // look for local searchform template
  $search_form_template = locate_template( 'searchform.php' );
  if ( '' !== $search_form_template ) {
    // searchform.php exists, remove all filters
    remove_all_filters('get_search_form');
  }
}
add_action('pre_get_search_form', 'search_form_no_filters');