Film Viral Campaigns

With social media ever-growing, viral marketing campaigns are adapting. There's been many, many attempts to ignite buzz about an upcoming film, with only a handful being genuinely successful.
The idea of a viral campaign is to generate word of mouth and further advertise a film. Because of the recent growing population of sites such as Facebook and Twitter, many choose to advertise through such websites.

Some earlier campaigns include Fight Club (1999) and The Blair Witch Project (1999).  Fight Club hosted a promotional website and a couple of 'public service announcements', which didn't do too great considering this was all before the YouTube era!
On the other hand, The Blair Witch Project's various police reports and backstory of the movie were largely successful because of the already existing interest in the paranormal; blurring the lines between fiction and reality.

Some more recent examples of viral marketing include Cloverfield (2008) and it's few websites detailing the backstory and characters form the film, including a fake MySpace account of the character, Sherlock Holmes (2009) and a Twitter account belonging to one of the characters of the film and The Dark Knight (2008).

The Dark Knight had 4 different websites apparently 'created' and 'vandalised' by the lead antagonist, The Joker. Each had hints toward the themes of the film and their characters.
This was one of the most extensive viral campaigns around, and considering the film made more than double the amount than its predecessor, it was one of the most effective.