When British economist Edward Hugh set up a blog that repeatedly predicted the euro could not survive, few people took notice. Not any more. With the European single currency facing its greatest challenge since it entered into general circulation in 2002 in the wake of the bailouts of eurozone members Greece and Ireland, his posts are now read by thousands of bankers, financial analysts and other policymakers around the world.

US securities regulators are looking at how investors trade shares in four privately held companies, according to reports, but the inquiry may broaden to the exchanges and trading platforms that facilitate these transactions, experts said.