"viral marketing" campaigns.... the rumors you reference of possibly being real, all staged by movie production company.

Except they managed to make it "viral" before social media so easily assists in making something viral. Using their own website, and then having the "actors"... fan the flames on chat rooms....

But this is a brillant idea:

"Perhaps the most compelling aspect of the viral marketing campaign was the attention to detail, to the extent that if you looked on the IMDb before the film was released, the three actors were listed as ‘missing, presumed dead’. They even handed out missing persons leaflets, although the posters put up in Cannes were taken down the following day when it was revealed that a television executive had actually been kidnapped, in an unconnected event."

The original viral marketing campaign. It paid off HUGE.