Volkswagen Brazil recently sponsored the biggest music festival in Sao Paulo, the (sold out) Planeta Terra Festival, where they decided to promote their coolest young car, the Fox, through a seriously good mashup of Twitter, Google maps and real world prize locations.
Volkswagen hid secret tickets across the entire city, and then displayed them on a microsite using Google Maps. The catch was, the map was zoomed all the way out and the only way to zoom in was to have the community band together using the #foxatplanetaterra hash tag, and the more tweets made, the more the map would zoom in, ultimately revealing the pinpoint location of each ticket. At which point it became a foot race in the real world to find them, day and night for 4 days.
In less than 2 hours, the campaign #hastag became the #1 trending topic in Brazil, where it stayed for the length of the campaign. Very cool promo mechanic from BBDO Brazil.