Trading in risky penny stocks is booming. Why it could be a sign of trouble ahead for the market. - MarketWatch
1. Penny stocks made up 47% of U.S. trading volume on June 12. 2. High-risk names surged, raising concerns about market frothiness. 3. 14 stocks in RUA rallied over 200%; most had no earnings. 4. Speculative stocks outperforming established companies indicate potential market tops. 5. Regulators warn of risks but interest from retail investors persists.