American Express stock is sliding this year, and the card company’s newest director just bought a large block of shares. American Express shares are about 12 percentage points in the red year to date, far worse than the In late January, the company reported strong fourth-quarter earnings and raised its dividend, but shares dropped as investors perceived weakness in the company’s guidance. Its stock fell again in mid-February after its chief financial officer said first-quarter revenue growth would be slower than in the fourth quarter.