Southampton will always struggle to a certain extent until there is a comprehensive and sustained media blitz in the local region - posters at all local railway stations, bus side advertising/bus wraps, taxi wraps, prominent billboards in the area, radio advertising and sponsorship to make people aware of the possibilities.
When BA City Flyer began flying from SOU, none of my immediate neighbours or any of my friends or family were aware of the new routes, and equally it's the same with the new EasyJet routes. Only a couple of weeks ago I mentioned to my next door neighbours that they could fly from SOU for their upcoming ski break - they had absolutely no idea they could fly with EasyJet from Southampton - they've now booked.
A bit of social media and the odd press-release to the Daily Echo or BBC South is not going to have the reach necessary to build awareness. Southampton Airport needs to spend very, very heavily to generate interest - speculate to accumulate!