Police are yet to ascertain the whereabouts of a German tourist reported missing while returning from a trekking expedition in West Sikkim last week.

49-year-old Hans Obeymeyer, part of a five-member trekking expedition, was 'mysteriously' missing when the rest of the team returned from their four-day trek near Yuksom, Deputy Inspector General (Range) Akshay Sachdeva said.

"However, our efforts are still on to trace him," Sachdeva told PTI, adding that a search operation led by Geyzing sub-divisional police officer, Mrinalini Shrivastava, is in progress.

Sachdeva did not rule out the possibility of the tourist having 'slid down' while the trekking team was on its way back.

"Considering that we have been in search of him for the last five days without success, we can't ignore rumours that Obeymeyer may even have died. Nevertheless, we will consider him missing until we recover his body," he said.

The other four members of the German trekking team, who had been detained by the police, were set free on Wednesday after they failed to provide any clue to Obeymeyer's whereabouts.

Sachdeva said that police did not suspect Obeymeyer's colleagues of having a hand in his mysterious disappearance.