Audience Extension Networks – A Guide for Advertisers

mediasense’s latest short-form guide demystifies Audience Extension Networks (AENs) – the third-party publisher networks that platforms like Google, Meta, and TikTok use to distribute ads beyond their own properties. This guide outlines what AENs are, their benefits and risks, plus practical guidance for advertisers to manage them effectively.

Key Takeaways

• AENs extend beyond owned platforms: Platforms open up external inventory through third-party partnerships.
• They expand reach but add complexity: Media plans benefit from greater scale across the open web.
• Brand safety and fraud risks increase: Suitability concerns and elevated ad fraud are common challenges.
• Auditing and opt-outs are essential: Regular checks and exclusion of AENs safeguard brand protection.
• Industry guidance is evolving: MediaSense and ISBA’s 2024 work offers new direction on AEN management.

Effectively managing open-web programmatic media -especially through auctions and DSPs – has long been a critical concern for advertisers. Yet, many overlook the fact that when campaigns are run on platforms like Google, Meta, or TikTok, ads may also appear across third-party sites and apps through their Audience Extension Networks.  

These AENs extend the reach of big media brands by leveraging relationships with external publishers and apps. While expanding reach, such networks bring inherent risks: reduced control over brand context, heightened susceptibility to ad fraud, and potential placement next to unsuitable content. MediaSense has been flagging these risks since 2021 in digital audits and advising clients to use platform settings to opt-out where appropriate.  

Concerns intensified with Google’s 2023 rollout of Performance Max campaigns and scrutiny over search partners—where brand safety in AENs became a hot topic in industry media.  

Responding to this landscape, MediaSense and ISBA in 2024 developed a clear, actionable guide for advertisers. It outlines how AENs operate, their strategic advantages, the risks they pose, and essential responsibility models—so advertisers and agencies can confidently manage both owned inventory and third-party extensions.

Report Highlights 

What Are Audience Extension Networks? 

• Third-party partnerships enabling ad delivery beyond platforms’ owned properties (e.g., Google using sites beyond YouTube, Search, Gmail, Maps).

Benefits of AEN Inclusion

• Expands campaign reach and frequency across the open web.
• Adds scale and diversity of ad placements beyond walled gardens.

Areas of Concern

• Potential brand safety and suitability risks.
• Increased exposure to ad fraud.
• Advertisers may unknowingly be buying from these networks if not carefully monitored.

Mitigation Best Practices

• Use digital audits to detect activity in AENs (MediaSense has been doing this since 2021).
• Adjust platform settings to opt out of extension networks when necessary.
• Build structured campaign governance around AEN inclusion decision-making.
• Collaboration between MediaSense and ISBA resulted in an industry-focused guide.
• Clarifies responsibilities for advertisers and agencies in programmatic media planning across owned and extended inventory