(Reuters) - Online retailer Zalando is focused on the growing sportswear category as it looks ahead to the Euros soccer tournament and Olympic Games this summer potentially driving sales of team shirts and activewear more broadly.

While Zalando's overall customer numbers fell in the first quarter, Chief Financial Officer Sandra Dembeck said the number of shoppers and the spend per person both grew in sportswear.

Along with beauty and children's wear, sports was the strongest segment for Zalando, which reported its multi-brand marketplace returned to growth on Tuesday.

"On sports, I would say the bigger moments are still ahead of us now with the Olympics and with the European Championships," Dembeck told analysts on a call.

Zalando, which sells apparel and trainers from sportswear brands including Nike, Adidas, and Puma, launched the premium sports brand On Running in the first quarter.

Sportswear brands are ramping up marketing investments into the Euros in Germany and the Paris Olympics, in the hope their visibility on the world stage will boost sales.

(Reporting by Linda Pasquini; Editing by Helen Reid and Emelia Sithole-Matarise)