call a theme template

I simply want to allow the output of a function to pick up a theme template within a module. The code below is what I have and I want web_hosting_article_directory.tpl.php to be picked up and used much like any other themeable function. I assume I am just missing something from the existing documentation but cannot find it for the life of me.

function article_menu($may_cache) {

  $items = array();
  $items[] = array(
    'path' => 'web-hosting-article-directory',
    'callback' => 'web_hosting_article_directory',
    'type' => MENU_CALLBACK,
    'access' => TRUE,
    );
  return $items;
}

function web_hosting_article_directory() {
    return theme('web_hosting_article_directory');
}

function theme_web_hosting_article_directory() {
    $output = '';
    return $output;
}