Following a beta test, Apple made the changes on 5 October after encouraging developers in the US to create a Search Ads campaign for their apps by offering $100 in credit.
Apple says more than 65% of all app downloads come from search results, while Search Ads can help users discover lesser-known apps that would not appear in the app charts.
Targeted ad campaigns can be set to start and stop on specific dates, or show only at specific times of the day. Apple is also offering data about campaign performance to track effectiveness with an array of metrics in a Search Ads Attribution API.
On its Search Ads web page, Apple says: "Designed to give users a safe search experience, Search Ads sets a new standard for delivering relevant ads while respecting user privacy."