The six had planned to descend the Yurungkax River, but disappeared shortly after setting off.
The 700-mile-long river is considered one of the most dangerous for rafting, and reaches speeds of up to 60 miles an hour in some places. No one has yet succeeded in navigating its entire length.
On Wednesday, searchers found several rafts and some equipment belonging to the team along the riverbank, but there has been no sign of the Russians since radio contact was lost shortly after they cast off.
The group had planned to raft the length of the river, which flows through the Kunlun Mountains, one of the longest mountain chains in Asia, but they failed to turn up 12 days later as scheduled.
The Russian Canoe Federation subsequently requested help from the Russian Embassy in China in finding the missing sportsmen.
Thousands of Chinese rescuers, assisted by Russian emergency teams, eventually began a systematic search of the river, without success.
Earlier, the Xinhua news agency quoted a local Russian-language interpreter as saying the Russian sportsmen might have been swept away by landslides or fallen victim to bandits who operate in the area.
The group was carrying 20 days worth of supplies, but those provisions will have begun running out by now assuming the six are still alive.
