By Mark Maurer 

Poshmark Inc. appointed an Amazon.com Inc. executive as its new chief financial officer as the online fashion marketplace works to boost the returns on its marketing investments.

The Redwood City, Calif.-based seller of secondhand goods on Tuesday said Rodrigo Brumana would become CFO, effective Dec. 1. Mr. Brumana has served as finance chief for Amazon's private-label business since last year. Before Amazon, he was CFO of used-goods marketplace OfferUp Inc. for about two years, and before that senior director of finance at e-commerce platform eBay Inc.

His appointment is the latest instance of a former Amazon executive taking over another company's finance function. Dan Jedda, a former divisional CFO of Amazon's digital video, digital music and advertising businesses, late last year joined clothing subscription company Stitch Fix Inc. as finance chief. Home rental company Airbnb Inc., online map provider Mapbox Inc. and digital advertising firm Trade Desk Inc. also nabbed their CFOs from Amazon or one of its subsidiaries.

Kapil Agrawal, Poshmark's vice president of finance, stepped in as interim chief financial officer in August following the departure of Anan Kashyap after five years as CFO. Ethos Technologies Inc., an insurance-technology company, in September said it named Mr. Kashyap as its first finance chief.

Poshmark, which went public on the Nasdaq in January, in recent months has faced headwinds stemming from Apple Inc.'s privacy changes and higher competition from other retailers. Apple's new policy, rolled out in April, requires apps to ask users if they want to be tracked. Many users have opted out of tracking by popular apps, resulting in those apps getting less data on consumers' habits and interests, which means they can no longer target them as effectively with ads.

Last week, Poshmark said its revenue grew 15.8% to $79.7 million in the third quarter compared with the prior-year period, as consumers ramped up spending. The company also reported a net loss of $7.2 million, compared with a profit of $10.8 million a year earlier. It recorded its first profitable quarter in the period ended June 30, 2020.

The company declined to comment beyond its release and filing.

"Poshmark has a long runway of opportunity ahead, and with Rodrigo's extensive experience, we will continue to accelerate growth and achieve our vision to build a more seamless, more social, and more circular way to shop," Manish Chandra, chief executive of Poshmark, said in a statement.

Mr. Brumana is set to receive an annual base salary of $467,000 and will be eligible for a sign-on bonus of $250,000 and a discretionary performance bonus of up to 50% of his annual base salary, according to a regulatory filing.

Mr. Brumana will likely focus on finding new ways to improve the return on the company's marketing investments, which are key to attracting new customers, said Tom Nikic, senior vice president for apparel and footwear equity research at financial-services firm Wedbush Securities Inc. The company's marketing expenses of $36.4 million represented 45.7% of its total revenue for the latest quarter, up about 18 percentage points from the prior-year period, filings show.

"If they can't lower their customer acquisition costs or the cost of retaining customers, it's going to be hard to generate consistent profitability," Mr. Nikic said.

Colin Kelaher contributed to this article

Write to Mark Maurer at mark.maurer@wsj.com