Shortcode for small buttons

You may get a customized code from here: https://www.addthis.com/get/sharing

or use this in the template/theme file

do_action( 'addthis_widget', get_permalink(), get_the_title(), array(
                                'size' => '16',
                                'services' => 'twitter',
                                'preferred' => '3',
                                'more' => true,
                                'type' => 'custom',
                                ));

The size-parameter have no effects. How i can setup the buttons bigger?