The S&P 500 (SNPINDEX:^GSPC) declined more than 2.5% last week, prompting many investors to start looking for the exits in anticipation of a more substantial drop. Yet even as investor confidence fell through the floor, a few stocks managed to gain ground on the week, with Facebook (NASDAQ:FB), Archer Daniels Midland (NYSE:ADM), and CH Robinson Worldwide (NASDAQ:CHRW) proving to be the most successful stocks last week.

Facebook rose more than 3% as investors couldn't decide whether the social-media giant is a momentum stock or a high-growth prospect with huge future potential. On one hand, Facebook still has a pricey valuation, and even though it's considerably lower than many of its smaller peers, Facebook's larger size makes it even more difficult for its stock to keep gaining ground from current levels. Yet many believe that CEO Mark Zuckerberg's recent acquisitions could help Facebook extend its growth long beyond the initial popularity of its namesake social-media service, turning Facebook into a much broader ecosystem that could produce even greater profits from both desktop and mobile users in the years to come.

Archer Daniels Midland also gained 3%, continuing to gain ground after getting an analyst upgrade late last week and a nearly 20% boost in price target to $50 per share. Despite a rough winter, the agricultural specialist is making moves to try to bolster its growth, with reports of plans to increase its investment in Australia's GrainCorp in the long run. As controversy over genetically modified organisms threatens the ability of U.S. producers to export their products in an unrestricted manner, it could become even more important for Archer Daniels Midland and other ag companies to extend their reach around the world and become locally important in a wider range of international markets.

CH Robinson Worldwide climbed nearly 5% as the logistics company and provider of freight-transportation services continued to rebound from its drubbing earlier this year. The plunge in early February came after CH Robinson Worldwide's fourth-quarter earnings report, in which the company reported a 5.6% drop in truckload-transportation revenue. But CH Robinson has done a good job of cutting back on its operating expenses, and on set of investment analysts upgraded the stock, believing that CH Robinson can increase its rates and boost its margins from rising volume.

Even when the stock market falls sharply, smart investors never stop looking for stocks that can be potential winners. A downturn can be a perfect time to look for the companies with the best fundamentals, especially if you get a chance to buy at a bargain price.