"We have done everything possible to find them, but (police) rescue official Andrea Mittner has announced this afternoon that the search has now been abandoned," Sandra Scianguetta, police spokeswoman for the eastern canton of Grisons, told AFP.
"We will not now be able to find anyone," Mittner was cited by Swiss media as saying.
The eight missing - four Germans, two Austrians and two Swiss - were hiking Wednesday on the Piz Cengalo mountain, near the Italian border, when the landslide struck, sending mud, rocks and dirt cascading down the mountain.
About 100 people were evacuated from the border village of Bondo, which was hit by the debris.
About 120 emergency workers equipped with infrared cameras and mobile phone detectors, helicopters and rescue dogs had been scouring a five-square-kilometre (1.9-square-mile) area of the disaster.
Dramatic footage from Wednesday showed an entire mountainside disintegrating, unleashing a mass of thick mud and sludge that tore up trees and demolished at least one building.
The landslide was so severe that the vibrations set off seismometers across Switzerland, measuring the equivalent of a 3.0-magnitude earthquake, according to the Swiss Seismological Service.
Experts suggested that climate change could be partially to blame for the disaster, with melting permafrost and an adjacent glacier likely destabilising the landmass.
There could be more landslides in the area, local geologist Andreas Huwiler warned.