According to the BBC and other reports listed below, Gui Minghai, the Hong Kong-based publicist, writer, scholar, and owner of a political bookstore, and three associates in Hong Kong have been "disappeared" (arrested-unconfirmed), apparently for publishing things inconvenient to somebody in China. Apparently, several weeks ago, Gui was kidnapped/taken from his vacation home in Thailand, by Chinese police. The circumstances are unclear; I am not aware of any Thai commentary yet; and no journalist seems to have been able to get any confirmation from any Chinese authorities (of course, a familiar pattern in Chinese "disappearances").
Mr. Gui Minghai is also known by his nickname Ahai, and is a Swedish citizen. I knew him in China, and in Sweden, where he earned an MA degree at Gothenburg University, and I last saw him in Hong Kong in 2012.
His name Gui Minghai has been miswritten as "Gui Haiming" by the Guardian and by the RFA which apparently mis-transcribed his name from its own RFA Chinese service, where it is rendered correctly as Gui Minghai, and correctly with the nickname Ahai. Sadly this error is now being circulated by other media (again, "as usual").
For the best report, see BBC News 10 November 2015, http://www.bbc.com/news/world-asia-34782266 ("Hong Kong bookstore disappearances shock publishing industry")
And also see, on the alleged Chinese police-engineered kidnapping in Thailand:
http://en.boxun.com/2015/11/06/hong-kong-publisher-kidnapped-in-thailand-and-returned-to-c... (some places miswrites Gui Minghai as Gui Minhai)
http://www.rfa.org/english/news/china/missing-11062015110112.html (name miswritten as "Gui Haiming")
http://www.rfa.org/mandarin/Xinwen/2-11062015102817.html (in Chinese, name correct)
http://www.theguardian.com/world/2015/nov/09/hong-kong-publishers-gui-haiming-lu-bo-zhang-... (name miswritten as "Gui Haiming")
http://www.relatest.com/20151110664126976999993344/ (link to the Guardian)
http://www.kui.name/event/2015-11-07/銅鑼灣書店老闆+遊泰離奇失聯_n1211914.htm (in Chinese)
The best Swedish report so far (although citing the misspelled name):
--Magnus Fiskesjö (Associate professor, Dept. Anthropology, Cornell University)