21/09/30 12:06:50.55 GvuBtalq.net
Mr Shishov left his home on Monday morning and it was assumed he had gone for his daily jog as his running gear was not found there later, his colleagues said.
They conducted their own search of the woods where he usually went running. Mr Shishov had felt under constant surveillance since he left Belarus last year, they said.
One colleague, Yuri Shchuchko, told Current Time TV that police said Mr Shishov had marks on his face, suggesting that he had been beaten up.
Mr Shchuchko said Ukrainian security officers and police had privately warned the BHU about threats to activists.
"They said we should watch ourselves because a Belarusian KGB [secret police] network was active here," Mr Shchuchko said.
The BHU said in a statement: "We were warned repeatedly by local sources and our people in Belarus about possible provocations, going as far as kidnapping and assassination. Vitaly reacted to those warnings with stoicism and humour."
On its website, the non-governmental organisation says it provides support to new arrivals in finding accommodation, jobs and legal advice.
At a briefing, Ukraine's national police chief Ihor Klymenko said Mr Shishov was found with grazes on his nose and knee. But the police chief said it was too early to determine whether he had been attacked.
Mr Shishov had not reported his suspicion of being under surveillance to the police, Mr Klymenko said.