Instagram has been crowned the most effective social marketing tool, overtaking Twitter, Facebook and YouTube. The site delivers more sales and consumer actions than other social platform, according to a study which documented the 15 biggest influencers on consumer behaviour. Millennials were found to be the group most responsive to posts on the image sharing app, with 68% of 18-24 year-olds saying they more likely to purchase an item if someone they followed on Instagram shared it.