ICYMI: Twitter stock gained 2 percent early Friday after the social media giant late Thursday said that CEO Dick Costolo will step down amid growing criticism of the company's financial performance. Co-founder Jack Dorsey, who served as CEO during Twitter's early years, will temporarily take the reins. Shares closed little changed at $35.90.

By the letter: Citrix Systems jumped 7 percent, to $70.39 Thursday after the software company received a letter from investment firm Elliott Management proposing a shake-up in strategy. The company's stock ended the week at $ 71.91.

No bananas: United Natural Foods, a supplier to Whole Food Markets and other stores, slumped 4 percent Tuesday, to $61.01 after it posted results that fell short of analysts' targets and cut its full-year profit. The company's stock closed the week at $62.70.

Thin air: Several airlines saw their stocks dip Monday after the brokerage Raymond James cut sector earnings forecasts, saying carriers would struggle to raise fares as much as anticipated. Delta Air Lines dropped 5 percent, to $40.75, closing the week at $41.14. American, which dropped 4 percent to $39.86 Monday, landed Friday at $40.71.

Splitting up? Johnson Controls jumped 4 percent Wednesday, to $53.73, after the company said that it was considering a sale of its automotive business. The company's stock finished the week at $52.35.

Good dose: Amgen rose 1.5 percent, to $157.96 Thursday after a panel of advisers at the U.S. Food and Drug Administration recommended approval of a cholesterol-lowering drug for people at especially high risk of clogged arteries. Amgen closed Friday at $156.12.