Newspaper publisher Gannett Co. has doubled the number of staffers at its product-review website over the past 18 months, looking to expand its digital reach as print advertising and circulation revenues face continued pressure.

The Gannett site, called Reviewed, is taking direct aim at Wirecutter, a popular products-review site owned by the New York Times Co. , and BestReviews, a similar rival that Nexstar Media Group Inc. acquired last year for $160 million in cash. Gannett operates more than 250 newspapers, including USA Today.

The push comes after e-commerce surged and ad spending declined for a time during the Covid-19 pandemic, increasing pressure on media organizations to hunt for new revenue streams and to shore up their digital businesses.

“Top-line revenue has grown 50% every year for the last three years, and our projections for 2021 are around the same percentage,” said Chris Lloyd, general manager of Reviewed. He declined to provide dollar revenues.

Mr. Lloyd said the site’s staff has increased to 80 full-time employees. Most new hires are editors and writers who work at the company’s 25,000-square-foot testing lab in Cambridge, Mass. Reviews are published online at Reviewed.com and across the USA Today Network, meaning any of Gannett’s newspapers can run articles written by Reviewed staffers.

“ ‘Everything starts from our lab in Cambridge. We wave our nerd flag proudly.’ ”

— Chris Lloyd, Reviewed general manager

Gannett acquired Reviewed in 2011 when it was an advertiser-driven site. Six years later, it began to focus instead on affiliate marketing fees, which it earns when a reader clicks on a product link, is directed to a seller’s website and then makes a purchase. Fees range from 1% to 20%, depending on the category, said Mr. Lloyd.

Digital publishers have experimented with affiliate marketing for years, and a number of dedicated product-review sites are already well-established and trusted by consumers. Reviewed competes with at least half a dozen major rivals, said Mr. Lloyd, as well as websites that offer limited product reviews with affiliate links.

E-commerce sales in the U.S. are expected to increase 16% to $918 billion this year, according to Forrester Research Inc. Forrester analyst Sucharita Kodali said independent product-review sites are likely to gain favor with consumers concerned that some reviews on large retail sites might not be authentic or trustworthy.

“These sites represent an additional revenue stream without requiring an investment in inventory or large advertising sales forces,” she added. “It’s generally high-margin revenue.”

Last December, when Nexstar disclosed its purchase of BestReviews, Tom Carter, Nexstar’s president, chief operating officer and chief financial officer, said, “We are acquiring a fast-growing digital product review company with a profitable and scalable business model.”

A diversified media company, Nexstar owns or operates 199 TV stations across the U.S. BestReviews depends on affiliate sales for its revenue and doesn’t carry paid advertising.

New Media Investment Group Inc. acquired Gannett in November 2019 and combined its assets with GateHouse Media. The new company took the Gannett name. In May the company said it had more than 1.2 million digital subscriptions, a figure it is seeking to raise to 10 million by 2026.

Gannett is betting that its digital push can help stem declines in its traditionally print-focused business. Its first-quarter revenue fell 18% from the same year-earlier quarter, to $777 million, while its loss attributed to Gannett widened to $142.3 million, or $1.06 per share, from $80.2 million, or 61 cents a share, in the year-ago quarter.

The New York Times doesn’t break out revenue at Wirecutter, which it acquired in 2016. However, the company noted in February that a fourth-quarter revenue decline in a reporting group that includes television and film activities was partially offset by gains in Wirecutter affiliate-referral revenue.

Some executives see further opportunity in product-review sites beyond affiliate revenue. Meredith Kopit Levien, chief executive of the Times, said the company expected to “test the possibility of a subscription product for Wirecutter” this year. A spokeswoman for Wirecutter declined to comment further.

Mr. Lloyd said Reviewed has an opportunity to carve out its own brand identity and devoted following. He sees rival Wirecutter as “the cool friend that gives product reviews; we’re the nerdy friend. Everything starts from our lab in Cambridge. We wave our nerd flag proudly.”

Write to Jeffrey A. Trachtenberg at jeffrey.trachtenberg@wsj.com