EBay Inc. and Amazon.com Inc. sales growth slowed in September, signaling that consumers may not increase holiday spending as much as expected, said Herman Leung, an analyst at Susquehanna Financial Group.

EBay’s comparable sales rose 21 percent in September from a year earlier, less than August’s 24 percent growth, Morrisville-based ChannelAdvisor said earlier this week on its website.

Amazon’s growth rate fell to 37 percent last month from 41 percent in August, ChannelAdvisor, a provider of e-commerce services, said. Comparable sales measure revenue for merchants who have used the site for at least a year.

“This holiday season could start off slow,” Leung, based in San Francisco, said yesterday. “September is a preview. The confidence level has gone down a little bit, looking at this data.”

New advertising options from Google Inc. that let merchants include more product information in search ads — such as prices and images — may be adding to the decline, Leung said. The ads could be filtering buyers to the direct sellers doing the advertising instead of e-commerce companies such as Amazon and EBay. Consumers also may be paring back spending as they prepare for the holidays, he said.

Online Storefront

Amazon, the world’s largest online retailer, is increasingly adding third-party sellers to its site and, at the same time, wooing customers with its proprietary Kindle e- readers. Those sales contributed to total e-commerce spending that rose 15 percent in the second quarter from a year earlier, according to research firm ComScore Inc.

EBay is moving away from auctions and focusing more on fixed-priced sales to drive growth. Auctions declined 17 percent in September from the previous year, while fixed-price sales rose 24 percent, according to ChannelAdvisor. ChannelAdvisor’s software helps third-party sellers manage online sales on e- commerce sites.

EBay redesign

Meanwhile, on Thursday, EBay unveiled a redesigned website to encourage visitors to browse and collect items they might want to buy later with something it calls the “feed.”

The feature, reminiscent of popular sites like image-heavy Pinterest, shows users items based on things they purchased in the past or items they’ve clicked on the site. Shoppers can also edit their feed by adding or removing categories and individual items.

Ebay’s old search feature — which helps shoppers who already know what they are looking for — is not going away. Rather, the company says it wants online shopping feel more like window-shopping or browsing in a brick-and-mortar store.

San Jose, Calif.-based eBay Inc. unveiled the new site Wednesday at an event in New York’s trendy Meatpacking district. It will be available to eBay’s U.S. users gradually over the next 100 days and to international users after that. EBay says it has 105 million active users worldwide. And it has about 25 million sellers ranging from large brands to individuals.

The company is also launching a smartphone and tablet computer app called eBay Now. The app lets people order items from retailers such as Macy’s, Target and Walgreens. In most cases, eBay promises delivery within an hour. eBay Now is being tested in San Francisco but the company will likely roll it out elsewhere in the future.

The company also simplified its shopping site so that it takes fewer clicks of the mouse to buy items. The redesign also looks cleaner and with larger photos than the previous version.

In addition, the company has been testing a service called Lifestyle Deals, which offers Groupon-style daily deals in select cities such as San Francisco, Boston and New York.

(Bloomberg and The AP contributed to this report.)