The problem of quickly, capillary and effectively spreading information over social networks has become extremely important in many areas of our society. This problem has been widely studied in the recent literature and is still open, but it becomes even more challenging, due to the new issues to deal with, in a multi-social-network context, where the possibility that information can cross different social networks has a fundamental role. As a matter of fact, this is the scenario towards which social networks are evolving with a rapid increase of the mutual interaction among them. In this new scenario, called Social Internetworking Scenario (SIS, for short), we propose an approach devoted to favor information spreading, by identifying two stereotypes, specific for SISs, which are expected to be good spreaders: the starter and the bridge.