Here are 10 ETFs (from a universe of over 1,000 funds) with the highest percentage increase in shares outstanding in the past month (through June 17). Of them, all but SPLV have been trading for at least six months.
Most interesting among them is BZF, Wisdom Tree's Brazilian Real currency ETF, which has been trading for over three years but last month more than doubled in assets (share prices went up only a few percent in that same time). Also interesting is XIV, the VelocityShares ETN that tracks the inverse of the volatility index (sort of an inverse of the VXX, the flaws of which I've documented). The XIV is only about 1/10th the size of its evil twin the VXX, but at this rate, perhaps it'll become a viable alternative to the short VXX trade.
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Disclosure: I am short VXX.