The cities around the world are concentrating the social life around the world. Nowadays our manner of socialization is changing. The emergence of social networking sites, have enabled greater social connectivity, which in turn has allowed the distances between people to be reduced and interactive dynamics to be generated until recently unpublished. This social phenomenon generates large amounts of data, attracting the interest of researchers and academics and is called Big Social Data. Access to these massive amounts of data makes it possible to detect patterns of behavior that are not visible to the naked eye, simply because they can radiate unknown connections to the naked eye. In addition, it is a type of data that, being more or less accessible, in front of others, does not bother the citizens because they are captured without people feeling observed, granting a very important spontaneity in the collection of data. Despite the many expectations it generates, we must qualify that Big Data does not explain things by itself. The voices that warn that Big Data has a lack have been intensified: explain why, the reasons why users of services do what they do, the emotions, feelings and realities that determine their behaviors and attitudes. To cover this gap, Thick Data is needed, that is, the "dense description" of information as a method to analyze phenomena, cultures and relationships between people. In short, it is about understanding that Thick Data and Big Data are complementary tools that have to be used in a balanced way. In the present communication we will show different examples of research with Big Social Data made so far. In that sense, we have investigated the capacity of organization and mobilization that can help to face social emergencies as disasters and catastrophes. As example we will demonstrate how people organized to find victims facing a terrorism attack happened at Strasbourg (France).