US TV
The group has teamed up with the Red Cross and say more than 3,000 people are going to take part.
Fans are hoping to convince CBS to order another season, though The Hollywood Reporter says it was already likely to return.
Their campaign has, however, persuaded Moonlight star Alex O'Loughlin to become an official spokesman for the Red Cross.
Barbara Arnold, one fan taking part, said: "We wanted to celebrate the return of episodes and really focus attention on the show. They say one pint of blood saves three lives. So if we can collect 3,000, wouldn't that be nice?"
Moonlight airs on Living in the UK.
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