What I recommend you do is give it a good title.
THE SCARIEST THING YOU WILL EVER SEE
DON'T WATCH THIS
WARNING, NOT FOR THE EASILY FRIGHTENED
THE MOST HORRIFYING CRIME OF THE CENTURY
^ Something along those lines ^
You can then put some money into promoting this thing on Youtube. You can pay money for this to be seen as an advertisement, or to see it on the front page of Youtube. And really, who can resist? Start a campaign for the film, revealing very little. But every once and a while, post a clip of something freaky.
But it has to live up to the hype. Perhaps have a normal scene, then $#!t hits the film, or there's a scene of someone walking around in the dark, and there's a couple of scares. Perhaps a dolly shot of the camera going towards a door, going into a room, then doing a slow pan, showing the room, then at the last second something popping up.
Oh, you could have a dolly in on a character, and him/her slowly turning around, and right before we see his face there's a loud bang and we cut to a title. You then have text saying something along the lines of VISIT www. (site).com TO SEE THE FACE. You then have info on the film's online release.
I recommend doing something along those lines.