Justin Timberlake is using his new video to seek out a romantic fan who used the song to soundtrack his marriage proposal.

The documentary-style promo for Not a Bad Thing, which Timberlake premiered on The Ellen DeGeneres Show in America on Thursday (20Mar14), was inspired by the story of a man who played the song as he asked his girlfriend to marry him on a train bound for Long Island in January (14).

The video, which doesn't feature Timberlake, serves as a search for the couple - a re-enactment of the proposal leads into footage of fans posting up flyers seeking out the pair.

A voiceover at the start of the five-minute film says, "We don't know who these people are or what their story is, but maybe you do. We're making a documentary about finding love. Have you seen this couple?"

The video also features real-life couples sharing their reflections on love and marriage.

The promo ends with the message "To Be Continued..."

After airing the film for the first time, DeGeneres told viewers, "Obviously, if you know this couple, contact us, because Justin is trying to find you and we'll put you all together."