FAQs

A custom audience is a group of people Meta lets us target based on how they've already interacted with you.For example, everyone who's watched a certain amount of one of your video ads, visited your website, or engaged with your Instagram/Facebook profile. It's often called "retargeting" because you're reaching people who've already shown some interest, rather than complete strangers.

There are several sources we can build a custom audience from, and we'll usually pick whichever fits the campaign goal:Video views: anyone who watched a set percentage (e.g. 25%, 50%, 75%, 95%) of a specific video you've run as an ad. Great for retargeting people who showed genuine interest but didn't convert.Instagram or Facebook engagement: people who've interacted with your profile: liked, commented, saved a post, sent a message, or visited your profile page. Broader than video viewers, and not tied to any one piece of content.Website visitors: anyone who's landed on a specific page (e.g. your Amazon listing, if you have the Meta Pixel installed there, or a landing page you control). Requires tracking to be set up in advance, so it only starts collecting people from that point forward.Customer list upload: a list of existing emails or phone numbers (e.g. your newsletter subscribers) that Meta matches against its own users, so you can advertise directly to people who already know you.App or event activity: relevant mainly for businesses with an app or e-commerce checkout events; less commonly used for author/publisher campaigns, but included for completeness. For book marketing specifically, video views and Instagram/Facebook engagement tend to be the two most useful sources, since they capture people who've shown real interest in you or your content without requiring separate tracking setup like a pixel does.

A lookalike audience is a brand new group of people Meta finds for you, based on shared characteristics with an existing audience (the "source"). For example, if we create a lookalike from your Instagram engagers, Meta analyses what those people have in common and finds other Facebook/Instagram users who look similar - the idea being they're more likely to be interested in your book too, even though they've never interacted with you before.

When we create a lookalike, we choose a percentage (usually 1–10%) of the total population in a chosen country. A 1% lookalike is the closest match to your source audience (smaller but more precise); a 10% lookalike is broader (bigger reach, but a looser match). We typically start narrow and widen only if needed.

No and this is a common point of confusion. A custom audience (like video viewers) genuinely grows as more people watch your ads and qualify for it. A lookalike is generated at a point in time from the source audience and doesn't accumulate the same way - its size is really a fixed percentage-of-population figure, not something that fills up.

Not precisely as a "current headcount" the way we can with a custom audience. Meta shows an estimated size range for lookalikes rather than an exact, constantly updating number. For reporting purposes, we focus on the custom (source) audience size, since that's the number that meaningfully changes over time.

Video viewers are specifically people who watched a set percentage (e.g. 25%) of one of your video ads. Engagers are people who've interacted with your Instagram or Facebook profile more broadly (likes, comments, profile visits, saves). They are not filtered by whether they watched any particular video. They're two separate custom audiences built from different sources, so their numbers won't match and shouldn't be added together.