BuddyPress.org

I can see potential problems with that $args variable you have setup.
Try setting up the arguments as an array.

$args = array( 'recipients' => $user_id, 'sender_id' => 11, 'subject' => $title, 'content' => $message );

If PMs are disabled, the code will not run. In fact, most likely you’ll get an undefined function error.