Dozens of ethnic Uighurs have disappeared since being detained in the wake of the riots in China's Xinjiang region, a human rights group has said.
Human Rights Watch said the 43 men and teenaged boys were taken in police sweeps of Uighur districts of Urumqi, and had since vanished without a trace.
"The cases we documented are likely just the tip of the iceberg," said Brad Adams, Asia director at Human Rights Watch.
The rights group is calling for the Chinese government to give details of everyone it is holding in detention.
In a report on the disappeared people, HRW said the police had searched two Uighur areas of Urumqi immediately after the riots. At least 43 people were taken away and had not been heard of since, it added.
"According to witnesses, the security forces sealed off entire neighbourhoods, searching for young Uighur men," the group said.
HRW said most of those taken away were young Uighur men in their 20s, although the youngest are reported to have been 12 and 14.
In many cases, families had been unable to find out what had happened to their relatives, said Human Rights Watch, whose report was based on interviews with local people.