The short film includes two new, digitally-enhanced images of how the missing girl might look now, at age six, more than two years after she vanished while on vacation with her family in a resort in May 2007, a few days before her fourth birthday.
One of the images shows McCann with fair skin, and the other with tanned skin and dark hair -- what she might look like if she's being held in Africa or the Middle East.
The appeal was launched Tuesday by the U.K. Child Exploitation and Online Protection Center (CEOP). Detectives hope the video will "prick the conscience" of someone close to the girl's abductor.
Watch the new video
"We know that there is someone out there who knows who's involved in her disappearance," CEOP chief Jim Gamble says in the film. "They may be keeping this secret out of fear, misplaced loyalty or even love. Keeping this information secret only increases the anguish of Madeleine's family and friends and increases the risk to other children. If you know who is involved and you're keeping this secret, remember that it's never too late to do the right thing. We urge anyone who knows anything about the whereabouts of Madeleine or who has information regarding her disappearance, to do the right thing now and give that information to their local police."
Madeleine's father, Gerry McCann, told the BBC on Tuesday the video is more of an attempt to contact specific people rather than appeal to the public for information.
"We need it to be spread far and wide, and for those people to be exposed to this message as many times as possible," he said.
The video is available in English, Arabic, French, German, Italian, Portuguese and Spanish. Police hope people will spread the film by way of blogs, e-mail and social networking sites.