The three-week campaign was booked by Mindshare and created in-house by Future, which owns SFX.
The site features a specially created desktop calendar that counts down to the launch of the new show.
Users can download the calendar to their PC, allowing them to receive regular updates about the show through articles, photos and trailers.
The campaign on also features an interactive map of the UK's scariest places, including haunted castles, ghostly sightings, grisly locations and mysterious happenings.
Users are invited to submit their own scary places and stories.
The map will remain on SFX.co.uk after the 21-day campaign ends.
The SFX website will also get a complete "'Demons' takeover" from Christmas Eve until the show debuts on Saturday January 3.
'Demons' is set above and beneath the streets of modern-day London, and follows a character called Luke, who is destined to fight vampires.
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