When it comes to risk management and emergency response, having an informed citizenry through mass media is not enough. Prior to the onslaught of typhoon Yolanda (Haiyan) in the Philippines, a great majority of Filipinos received warnings from mass media but disaster risk had hardly been mitigated. This paper explores social media, particularly Facebook, as a more suitable communication platform which local governments units (LGU) in the Philippines could take advantage of. It attempts to explain the nature of social media and their technological affordances, discuss the communication needs of people at risk met by social media, and identify the key functions of social media in times of crisis. It also discusses how Facebook was used for flood risk management and emergency response in the first class municipality of Cainta, Rizal within the week of the town-wide floods caused by typhoon Mario on September 19, 2014 which displaced 5,300 families. This paper concludes that social media, Facebook in particular, afford users a high degree of social presence, making them the best tool for creating and nurturing small online communities managed by LGUs. They provide strong support for social interaction, social integration and the strengthening of bayanihan (heroism) spirit.