Were aircraft flying over the areas? It is possible to use a piece of metal (like roof flashing-has to be shiny though-a piece of broken glass or a mirror would work), and flash an SOS at passing planes, helicopters, etc. I think it's "long, short, long".
I know that is the last thing people would think of in this kind of situation, but I'm going to remember it.
Could people still be actually on roofs? With the amount of choppers in the air (media, medical, searchandrescue), how could this be? And with the glut of choppers, why not post a five hundred cash reward for every person brought in?