If you've already called to let someone know that they are there and no one's shown up, I'd call the local news media folks whom are already crowded around the beach areas and let them know. I'd have a plan of action to search and rescue them myself if no one else would, and let the media, (ah hem) get wind of the rescue. Maybe I'd make another phone call and suggest that I was hoping someone was on their way to rescue them since the media was booking out there, and what a great image that would be on all the news channels, youtube, all our hard earned tax dollars at work...