At Stockpickr, we track daily portfolios of stocks that are the biggest percentage gainers and the biggest percentage losers. Stocks that are making large moves like these are favorites among short-term traders because they can jump into these names and try to capture some of that massive volatility. Stocks that are making big-percentage moves either up or down are usually in play because their sector is becoming attractive or they have a major fundamental catalyst such as a recent earnings release. Sometimes stocks making big moves have been hit with an analyst upgrade or an analyst downgrade.