I got a chance to use drupal form '#autocomplete_path' attribute to my one of the project.
Example usage :
// Autocomplete field
$form['autocomplete'] = array( '#type' => 'textfield', '#title' => 'Autocomplete field', '#description' => 'Autocomplete field example', '#autocomplete_path' => 'article/autocomplete', );
I have found one good resource about it at http://www.coalmarch.com/blog/autocomplete-drupal-form-tutorial
It may be useful to you. Happy coding :)