The stunt was orchestrated by Monument PR to promote tomorrow's Friday the 13th launch of console game 'Resident Evil 5', a zombie and gore-focused title.
The stunt involved a treasure hunt in which around 50 members of the public had to retrieve various legs, arms, heads and torsos from a number of secret locations.
A Monument PR spokesman insisted that the loss of the body parts was not a publicity-seeking appendage to the campaign's main body.
In the early hours of this morning, the parts were hidden in locations across a square mile of London, in places such as rubbish bins and on window ledges. More than 100 people signed up to participate in the event, which culminated in two of the heads, one torso and six limbs being returned by participants across the finishing line on Westminster Bridge.
However, one head, two torsos, and six limbs remain unaccounted for. A number of chicken livers, which were used for added gore, are also missing.
Before it transpired that body parts had disappeared, the stunt had already taken a turn for the worse when horrified passers-by complained to police. Officers were called to the finishing line, and organisers moved on, although no charges were made.
Monument is posting notices on various websites, as well as contacting media, encouraging anyone who finds body parts to return them.
A Monument spokesperson said: "If there is no news of them, we will have to inform the police."
The campaign reached its crescendo this week, when various websites targeting gamers posted information about the forthcoming treasure hunt. The competition was won by Steve Long, a 26 year-old IT consultant, who was awarded a prize of a holiday for two to Africa (where 'Resident Evil 5' is set).