Social media has radically altered how corporations market unhealthy products to young people. Social media influencers embody these shifts, and yet we know little about the nature or extent of their practices. Influencers are part of covert, under the radar marketing strategies unique to social media. These blur lines between user-generated and commercial content, making existing public health marketing regulations ineffective. Focusing on alcohol, tobacco, and vaping, this research will use innovative methodologies to explore influencer marketing on Instagram. An online survey of young people, aged 16-20 years, will identify key influencers. Influencers’ Instagram accounts will be examined using cutting-edge software to download and analyse posts and meta-data. We will then seek to interview key influencers. The research will enable us to trial these methodologies for effectiveness, and results could potentially transform national and global debates about the regulation of digital marketing and policy reforms needed to protect public health.