(Bloomberg) — Amazon.com Inc. unveiled a new advertising platform for mobile-applications developers, a push by the largest Web retailer to grab a bigger piece of the smartphone advertising market dominated by Google Inc. and Facebook Inc.

The service lets developers promote their apps on Android smartphones and tablets as well as Amazon tablets, paying Amazon each time a user clicks an advertisement displayed through the system. Campaigns start at $100.

“We work with many developers to support merchandising and advertising across our platforms and devices,” said Lyn Hart, a spokeswoman for Amazon. “We realized that many more developers would benefit from this advertising and merchandising.”

Amazon is a small player in the $28.7 billion U.S. mobile- advertising industry. The Seattle-based company has less than a 1 percent share of the market, compared with Google’s 35 percent and Facebook’s 17 percent, according to EMarketer Inc. Spending to market apps alone is projected to rise 80 percent this year to $3 billion, with Facebook leading that category.

Giving developers a place to showcase their apps gives them an incentive to develop programs specifically for Amazon, which makes the company’s devices and services more appealing to shoppers, EMarketer analyst Martin Utreras said.

“It will make the ecosystem more rich by having more apps,” he said.

Smartphone users are spending more time on mobile apps. The average user spent 153 minutes per day on mobile apps in April, up more than 20 percent from a year earlier, according to a report Wednesday by Cowen & Co.