Ümit Aslim, 39, set off on a trekking holiday in the high Himalayas back in mid-February.
His route was to take him through the Nepalese Annapurna Conservation Area Project (ACAP), home to two of the world's highest peaks, Annapurna at 8,091 metres and Annapurna II at 7,937 metres.
"We're really worried," Ümit's brother Marco told Bild newspaper on Sunday. He said he had not heard anything from Ümit since February 10th.
The last trace of Ümit after he set off is an entry from February 18th at a checkpoint along the Annapurna Circuit - a popular route with trekkers.
He had been due to fly back to Germany on February 21st but did not board his flight.
Concern for Ümit prompted Marco and his parents to contact the German mountain rescue organisation Rettungshunde für Nepal which has taken over the search.
The organization is collecting donations via its website to continue the search.
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