The vial was stolen on Saturday from the San Pietro della Ienca church in the mountainous Abruzzo region in central Italy.
The pope, who died in 2005, loved to go on skiing holidays there, according to the Repubblica daily.
Police and sniffer dogs are sweeping the area, famed for its weathered stone houses and the little church where the head of the Catholic Church once reportedly took refuge in a storm.
Pasquale Corriere, head of the "San Pietro della Ienca" association, said there are only three vials in the world containing the former pontiff's blood.
John Paul II and the Italian pope John XXIII, known as the "good pope", are set to become saints in a ceremony at the Vatican in April.
It is expected to draw hundreds of thousands of pilgrims.