Harley-Davidson Inc.’s Chief Executive Matt Levatich resigned Friday, leaving the motorcycle maker after years of declining sales and limited success attracting younger riders to its iconic brand.

Harley’s board said Friday that director Jochen Zeitz would serve as acting CEO and board chairman as it looks for a permanent chief executive. Mr. Zeitz will remain chairman when a new chief executive is hired, the company said.

“We will look to new leadership to recharge our business,” said Mr. Zeitz, a director since 2007 who replaced Michael Cave as chairman.

Harley remains the top U.S. motorcycle maker, but its annual domestic sales have fallen for five straight years—the entirety of Mr. Levatich’s tenure since taking the top job in 2015.

Harley’s motorcycle sales in the U.S. fell 5.2% in 2019, amid prolonged weakness in demand for the big, expensive touring bikes that make up the core of its model line. The company’s loyal base of baby boomer customers, who drove a Harley revival during the 1980s and 1990s, is aging and purchasing fewer new motorcycles.