A monitor displays Peloton Interactive Inc. signage during the company's initial public offering (IPO) across from the Nasdaq MarketSite in New York, U.S., on Thursday, Sept. 26, 2019.

Peloton shares plummeted as much as 12% in extended trading Wednesday after the fitness company reported mounting losses and slower revenue growth.

In its second earnings report since going public in September, Peloton said its net losses widened to $55.4 million, or 20 cents per share, from a net loss of $55.1 million a year earlier. Analysts had expected an even bigger loss of 36 cents per share, according to estimates from Refinitiv.

"At Peloton, we believe we can achieve both growth and profitability over time," Peloton CFO Jill Woodworth told investors on the company's quarterly conference call, adding that they expect to become profitable on an adjusted-EBITDA basis by 2023. "We're prioritizing our subscriber growth over profitability."

The company also said revenue rose 77% to $466.3 million from $262.9 million a year earlier. Analysts predicted total revenue of $423 million, according to estimates from Refinitiv.

Although the revenue growth topped predictions, it was a slower pace than in the prior quarter, when revenue more than doubled year over year.

Peloton also reported strong growth of its connected fitness subscribers, defined as a Peloton user with a paid subscription. Peloton reported more than 712,000 such subscribers at the end of the second fiscal quarter, up 96% from about 362,000 a year ago.

However, average net monthly churn, which Peloton uses to measure retention of connected fitness subscribers, grew to 0.74%, up from 0.52% a year earlier. The company said in its 2020 outlook that it expects churn to stay below 0.95% through the year.

The number of total members grew to more than 2 million.

Peloton is predicting revenue of $470 million to $480 million for the third quarter, and $1.53 billion to $1.55 billion total revenue for 2020.

The company also expects to add between 843,000 and 848,000 connected fitness subscribers for the third quarter and 920,000 to 930,000 connected fitness subscribers for the full year.

The company, which sells computer-connected fitness equipment and subscriptions to stream its workout classes, has reported strong revenue growth in the past, but has yet to post a profit.

Wall Street is growing increasingly skeptical of money-losing start-ups, with names such as SmileDirectClub, Uber and Pinterest among those that struggled in the public market last year. Mattress maker Casper priced its IPO Wednesday at $12 a share, giving it a disappointing valuation of $476 million. Its latest funding round had valued it at $1.1 billion.

Peloton also announced Tuesday that it settled legal disputes with Flywheel, a competitor that also produces stationary bikes with training programs, over alleged technology patent infringements. Hisao Kushi, Peloton's co-founder and chief legal officer, claimed the development as a "massive win" that "reinforces the strength of our patent portfolio," which is key for the company as it seeks to distinguish itself as more than a hardware company.

Peloton sells most of its products in the U.S., though it introduced them to the U.K. and Canada in 2018. Peloton also entered Germany in November last year.

Disclosure: CNBC parent Comcast-NBCUniversal is an investor in Peloton.