The one-and-a-half-minute appeal has been crafted by experts and psychologists to convince friends and family members of anyone involved in the young girl's disappearance to contact police.
It features the line "It is never too late to do the right thing" along with new pictures which show how Madeleine, who is now six, might look today.
Detectives believe people who know her location often search for her name online to track developments in the investigation. They hope the video will be widely spread over the web and become the top item when these people search for "Madeleine".
The video has been titled .
The Child Exploitation and Online Protection centre (Ceop), which instigated the appeal, is making the video available in seven different languages.
Speaking to the media to generate publicity for the appeal, Jim Gamble, head of Ceop, said: "We are using our network around the world to launch a viral message at one person."
The search for Madeleine has previously used ads in several formats including online video, TV, cinema and posters.
In the weeks immediately after her disappearance in May 2007 .
.jpg)
.jpg)