The two climbers, both in their 30s, were presumably swept into a crevasse in the avalanche prompted by the toppling ice, they said.
A French climber was found dead and four people were injured after the massive ice pinnacle -- known as a serac -- fell on Monday.
"The search is over," said Jean Ailhaud, the deputy prosecutor in the Alpine town of Bonneville. "Unfortunately there is no longer any point. They were most probably hurled into the crevasse which is now covered in 10 metres (32 feet) of snow," he told AFP.
This meant the two climbers had probably died of asphyxiation or hypothermia, he said. "It would be suicidal to try and climb down. The glacier will one day return the bodies," the deputy prosecutor added.
The two Germans had sheltered for the night in a mountain hut on the north face of the Mont Blanc, western Europe's highest mountain, when the serac broke off the glacier in the early hours of Monday at an altitude of 4,100 metres (13,500 feet).
Around 15 people were ascending the mountain at the time.
A rescue team with helicopters and dogs searching for survivors found the body of a 57-year-old Frenchman. A man and woman in their 40s, also French, were taken to hospital.
A 58-year-old Spanish national and his teenage son suffered fractures when they were hit by falling ice.
All other climbers present at the time of the accident were accounted for, except the two Germans.
Climate change has been blamed for falling rocks in the French Alps because of a thaw in permafrost -- the year-round ice found at high altitude that binds together giant slabs of rock.
Retreating glaciers, which are melting under the effect of higher temperatures, are also leaving the peaks more vulnerable.
