By 2018, though, mobile will have surged ahead as the dominant platform, accounting for 67% of social network ad spend. This rebalancing simply mirrors a more general trend in the UK of social network users flocking to mobile. eMarketer estimates that there will be 33.1 million social network users in the UK in 2014 and 26.2 million mobile social network users - a gap of 6.9 million. By 2018, though, mobile will have surged ahead as the dominant platform, accounting for 67% of social network ad spend. More than the travel industry simply following a general trend, there's also a more specific shift under way, with millennial travelers particularly predisposed to mobile and social. Get the full story at eMarketer