New Delhi, July 24 -- Shares of American Express Co. fell sharply on Friday even after the credit card giant posted stronger-than-expected second-quarter earnings and raised its full-year revenue growth forecast, as investors focused on rising expenses and higher spending on customer acquisition.

At 1:10 p.m. EDT, American Express shares were down 5.34%, or $18.20, at $322.64 in New York, marking the stock's steepest intraday decline in nearly five months.

The company, which primarily serves affluent customers, continued to benefit from resilient spending on travel, dining and other discretionary categories despite ongoing economic uncertainty. Unlike many card issuers that cater to a wider customer base, American Express has greater ex...