SAN FRANCISCO — Casper Sleep, a start-up that sells mattresses online, became on Thursday the latest money-losing outfit to get a cold shoulder from Wall Street investors.

The company’s stock began trading on the New York Stock Exchange at $14.50 a share, slipped below $14 in the afternoon and ended the day at $13.50. The lackluster first day of trading did not come close to fulfilling what Casper’s venture-capital investors thought it was worth a few months ago.

The New York-based start-up had been valued at $1.1 billion by private investors last year. But that was before the five-year-old company publicly revealed in January that it lost $67 million on $312 million in revenue in the first nine months of 2019, thanks in part to spending $114 million on marketing.

Casper reduced its proposed share price, valuing the company at less than $500 million. It raised $100 million in the offering.