The volunteer group leading efforts to find them, Euromaiden S O S, said 661 people were reported missing since protests began in December, and 272 remain unaccounted for.
Vitaliy Selyk, a coordinator of the group, said many were discovered in prison cells or hospitals, or resurfaced on their own after a breakdown in communications or loss of a cellphone.
He added he expected most to return home on their own, but beneath the hope lies a concern many Ukrainians may have been seized and detained by the Berkut riot police, by the pro-Russian provocateurs or by unofficial forces that worked to keep former Ukrainian President Viktor Yanukovych in power, the New York Times said Monday.
The concern is caused by two cases, the newspaper said, of seismologist and activist Yurly Verbytskyi, who was found dead in a forest after he was abducted from a Kiev hospital, and of protest organizer Dmytro Bulatov, who disappeared in late January and was found a week later, bloodied and showing signs of torture.
Two weeks since the last clashes in Kiev between demonstrators and authorities, many remain missing despite thorough checks of hospitals and prisons, and rumors are rampant, including a story that 50 opposition members were burned beyond recognition in a fire in the Trade Union building after they sought medical treatment there.
2014: The Year in Music [PHOTOS]