"This is an appalling use of Madeleine's picture and whether it is a result of hacking or a mistake it must be removed immediately," Mitchell said.
"Kate and Gerry are fully aware of this and are horrified."
The Web site, featured on VoucherDigg.co.uk, uses an image of Madeleine taken just hours before she disappeared while vacationing in Portugal with her parents five years ago. Lowcostholidays.com, the site promoting the vacation packages, says they are doing all they can to have the photo taken down.
Lawrence Hunt, chief operating officer at lowcostholidays.com, said the company had no contract with VoucherDigg.
"We discovered this vile material yesterday and immediately broke all the links to our site and contacted our lawyers," Hunt told The MIrror. "We apologize for any distress this may have caused."
The distressing discovery comes on the heels of the fifth anniversary of Madeleine's disappearance. The McCanns expressed renewed hope, inspired by a review of Madeleine's case by Scotland Yard, as well as a new photo of her digitally altered to account for her age since she disappeared just days before her fourth birthday.
"We would be really keen -- the general public helped us with the last age-progression -- so we would be really keen for them, really grateful, if they could circulate that image as far and wide as they can," Kate McCann said.
The McCanns are waiting to hear from Portuguese authorities as to whether or not the case will be reopened on their end.