Chinese discount e-commerce platform Pinduoduo Inc. reported better-than-expected second-quarter earnings Wednesday before the market opened, pushing the stock up 15%.

Pinduoduo said revenue surged 169% year-on-year in the quarter ended June 30, boosted by a robust user gain and increase in user spending over the year before.

The company reported an adjusted loss of 4 cents per share on revenue of $1.06 billion. Wall Street expected an adjusted loss of 19 cents on revenue of $878.8 million.

Average monthly active users grew 88% to 366 million. Active buyers in the 12 months ended June 30 climbed 41% to 383 million. Annual spending per active buyer in the 12 months increased 92% to $213.80.

Four-year-old Pinduoduo has emerged as the chief rival to market leader Alibaba Group Holding Ltd. in China’s trillion-dollar online retail market.

The company pursues a “group buying” model, in which buyers of groceries, electronic devices and other goods are encouraged to buy in bulk alongside friends and relatives to access discounts.

Pinduoduo held a $1.6 billion initial public offering on Nasdaq in July 2018. The stock surged $3.92, or 15%, and closed at $29.88 Wednesday.