The online campaign includes distribution of exclusive clips, talent interviews, advertorials and an extensive social networking drive.
Jam also conceived a partnership with Guardian.co.uk's dating service for a "screenmates" event, in which users of the dating site could win a chance to attend an early preview of the film followed by a drinks reception in central London.
Rebecca Lopez, brand manager at Guardian News and Media, owner of Guardian Soulmates, said: "Our members are fun, interesting individuals who like meeting other like-minded people for good dates.
"It's great to reward them with a special event like this and we think the films subject matter and offbeat style suits us perfectly."
Jam's creative team will also be handling all of the international media creative and media localisation for 15 countries for the release.
Fox Searchlight is a division of movie studios Twentieth Century Fox.
Kate Gardiner, marketing manager at Fox Searchlight/Twentieth Century Fox, said: "The partnership between '(500) Days of Summer' and Guardian Soulmates is a perfect example of Jam's creative thinking and their ability to deliver on bold ideas.
"They have consistently produced innovative and effective digital campaigns across a broad variety of film titles, from 'Juno' to 'Ice Age 3'."
'(500) Days of Summer' is due for release in the UK on September 2. The offbeat romantic comedy is about a woman (Zooey Deschanel) who doesn't believe true love exists, and the young man (Joseph Gordon-Levitt) who falls for her.