May 12 (Reuters) - Sportswear brand On ONON.N 49G.BN raised its profit margin forecast on Tuesday after strong first-quarter sales, as the Swiss company continues to gain ground in the sneaker and running shoe market long dominated by Nike and Adidas.

With 29-year-old actor Zendaya as a brand ambassador, co-CEO Caspar Coppetti said On is targeting younger, female consumers, adding that a clothing range launched with Zendaya in April is performing well.

First-quarter sales grew 14.5% to 831.9 million Swiss francs ($1.07 billion), beating analysts' average forecast of 822.5 million francs, according to data compiled by LSEG.

The brand now expects an operating profit margin of between 19.5% and 20% for 2026, up from 18.5 to 19% previously, and a gross profit margin of at least 64.5%.

Coppetti said profitability was helped by successful new sneaker launches, with the Cloudtilt - retailing at 190 euros - the best-selling shoe across Foot Locker Europe in March.

However, a strong Swiss franc hurt On's sales figures in the Americas, its largest market by revenue, with just 3.1% growth compared with a 32.7% rise a year ago. Asia-Pacific was the strongest region with 44.4% sales growth.

On has changed up its senior leadership, with co-founders David Allemann and Caspar Coppetti taking over as joint CEOs on May 1, replacing Martin Hoffmann. Frank Sluis - previously at supermarket group Ahold Delhaize - joined as chief financial officer at the same time.

"We're very happy to have found, with Frank Sluis, someone that comes from a just under $100 billion revenue company that can also help us unlock some of these economies of scale," Coppetti said.

($1 = 0.7797 Swiss francs)