best way to market a new product at a large event

hi guys, just looking for some advice here. without giving too much away about our product/service, we are launching at a large event which is over the course of 7 days, approx 700,000 people will be in attendance. our service is essentially mobile phone charging. now my question is what is the best way to market to these 700,000 people? i've been thinking about doing social media campaigns before and during the event, finding frequently used hashtags and responding to each of them w/ a basic "phone running low? check us out at xxxx location" in addition to this our social medias when clicked on will have a map of the event and where to find us. any ideas on the best ways to automate this process? or ways to improve it? what about completely different forms of marketing? any help is much appreciated.