Expanding audiences when first-party data hits a wall
First-party lists only take you so far. And this agency was starting to feel it.
They were running sophisticated, full-funnel campaigns using high-quality data. But their core audience had been hit one too many times. Performance was slipping, and growth had stalled. Adding more budget wasn’t the answer. Neither was spraying ads at broader segments and hoping for the best.
What they really needed was reach. The right kind. Especially among younger voters, who are notoriously tricky to engage and don’t respond well to blunt demographic targeting. And with limited room for error, they also needed to avoid duplication and wasted impressions.
The Science
Studies have shown that people are more likely to vote they way their friends and peers vote. Therefore, it’s easier to get resistant groups to vote. In this example, younger voters. If you can target people who are already seeing their peers register, the chance of them registering goes up significantly. This creates a domino effect, driving up overall registration from this cohort.
The approach
We helped rethink the strategy from the ground up, using behaviour instead of assumptions. Rather than segmenting by age or interests, we mapped out postcode-level communities where influence was already active. These were places where real-world social signals mattered more than audience labels. Where people were already hearing about their friends registering the vote, but needed the nudge over the line for themselves.
This was particularly valuable for reaching younger voters, who are more influenced by friends, peers and trusted networks than by traditional campaign tactics. Herdify’s data uncovered new areas with high potential, while avoiding any overlap with existing first-party activity. No guesswork. No waste.
The audience targeting list plugged straight into their current platform setup, running alongside existing campaigns. This made it easy to compare results side by side and keep the media plan simple.
The results
The impact was immediate.
On Instagram:
- Cost per click dropped 50%, compared to using first-party data
- Click-through rate hit 0.62%, nearly four times higher than the 0.17% base line
Facebook followed the same pattern:
- Cost per click (CPC) reduced by 14%
- CTR climbed 27%
The campaign beat every benchmark, Engagement was higher across the board, and Instagram was the standout, delivering triple the interaction of standard audiences.
Most importantly, the uplift wasn’t just cosmetic. It opened up a new channel to reach younger audiences who hadn’t been engaging before. With stronger signals of intent and more efficient spend, this test set the stage for future campaigns focused on turnout and mobilisation.
Why it matters
First-party data is powerful, but it’s not endless. And in high-stakes campaigns, you need more than reach. You need relevance.
This case proved that targeting based on behaviour, not just profile, is a more effective way to grow. The client gained access to new communities. They saw higher engagement. And they spent less doing it.
For marketers trying to activate younger audiences, the message is clear. If you want to drive action, you need to find people where influence already exists. You need to meet them in the middle of their community, not at the edge of your targeting parameters.
Testing this approach didn’t just improve performance. It gave the team a scalable way to build smarter, more responsive campaigns that can grow with their goals.
