At our Mobile Developer Conference on May 2nd, we announced a new targeting field for custom audiences that comes with our latest SDK, called 'App User ID'. Custom audiences let developers and marketers find their existing customers on Facebook. Using information you know about your customers, you can reach the right people on Facebook that you want to connect with. The process behind custom audiences protects people's personal information; learn more here.
In addition to leveraging current customers' hashed email, phone number and Facebook UIDs for custom audiences, you can now also reach groups of people who have taken actions in your app (such as installs or purchases) with relevant ads across both desktop and mobile. With App User IDs, for example, a retail app can reach people who have made a purchase in their app with additional items they may be interested in. Or a game developer can target groups of people who installed one of their games with another game that they are likely to play.