Existing customers share characteristics that can be used to find similar people. A lookalike audience is a group of potential customers generated by an advertising platform on the basis of similarity to a source audience—usually a company’s current customers, website visitors, or email list. The platform’s algorithms identify users who resemble the source on demographic, behavioral, and interest dimensions.

Marketers use lookalike audiences to expand reach beyond people who already know the brand while still targeting those statistically more likely to convert. The quality of the source audience strongly influences the quality of the lookalike. A source of high-value customers tends to produce better results than a source of casual browsers.

Platforms allow control over the size and similarity of the lookalike: smaller audiences are more similar; larger ones reach farther but with less precision. Testing different source lists and similarity levels is common practice. When the underlying data are strong, lookalike targeting can improve the efficiency of prospecting campaigns.