// Set to the current path so we can redirect back there after submit.
$form['submission_path'] = array(
  '#type' => 'hidden',
  '#default_value' => current_path(),
  '#weight' => -100,
);

$form['#action'] = url('search-callback');

function mymodule_search_callback() {
  return '';
}

// Redirect back to the page that submitted the search.
$form_state['redirect'] = array(
  $form_state['values']['submission_path'],
  array(
    'query' => array(
      'search' => urlencode($search-term),
    ),
  ),
);

$form['#submit'][] = 'mymodule_search_callback'

function mymodule_search_callback() {
   $form_state['redirect'] = current_path() . and your urlencoded serch term;
}