Lookalike audiences (called 'Similar Audiences' on Google Ads) are prospecting audiences built by advertising platforms to find new users who share statistical characteristics with an existing source audience — typically your best customers, highest-value purchasers, or most engaged website visitors. The platform analyses the source audience's behaviours, demographics, interests, and online activity, then identifies a much larger pool of users who match this profile. Lookalike audiences combine the performance advantage of audience targeting (reaching relevant users) with the scale advantage of prospecting (reaching users who have not yet discovered the brand).
Lookalike audiences have become a cornerstone of paid social advertising strategy because they outperform broad interest targeting while maintaining the scale that narrow custom audiences cannot provide. A furniture retailer's Customer Match list of 10,000 paying customers is powerful for remarketing but too small for significant reach. A 1-3% lookalike audience of those customers can reach millions of UK users with similar characteristics — combining the specificity of targeting known buyers with broad prospecting reach.
How to build effective lookalike audiences
- Choose a high-quality source audience — the best lookalikes come from your highest-value customers (highest LTV segment), not all customers
- Minimum source audience size — Meta requires 100+ people in the UK; larger source audiences produce better-quality lookalikes
- Value-based lookalikes — where platform supports it, provide purchase value data to create lookalikes weighted toward high-value customers
- Percentage tiers — 1% lookalikes are most similar to source (smaller, higher quality); 5-10% are broader (larger, less targeted)
- Exclude existing customers — always add existing customer lists as exclusions to avoid wasting prospecting budget on people who already purchased
- Test multiple sources — lookalikes from purchasers vs. email subscribers vs. website visitors may reach meaningfully different audiences
- Refresh regularly — stale lookalikes (source audiences not updated for 3+ months) drift from your current customer profile
Lookalike audiences consistently outperform broad interest targeting for conversion-focused campaigns. Industry benchmarks show lookalike audiences achieving 20-40% lower CPAs than equivalent interest-targeted campaigns for the same products. The performance advantage comes from the specificity of the source audience — the platform knows what your actual customers look like and can find others like them, rather than making broad assumptions based on declared interests. For awareness campaigns, interest targeting can be valuable for broader reach; for conversion campaigns, lookalikes are almost always preferable.
Google began phasing out Similar Audiences in 2023, officially stopping creation of new similar audience segments. Google's replacement is AI-powered audience expansion within Performance Max and Optimised Targeting in Display and Demand Gen campaigns — which achieve similar objectives (finding new users similar to converters) through Google's internal signals rather than explicit lookalike audience lists. For audiences reliant on Google's equivalent of lookalikes, transitioning to Performance Max with strong audience signals (customer lists, remarketing audiences) achieves a comparable prospecting effect.