Many politicians as well as journalists are using Twitter regularly and are connected on the microblogging platform. We use the agenda-building approach as conceptual background because political tweets can serve as information subsidies if they are used by journalists, indicating an agenda-building influence by politicians. It has not yet been systematically investigated which functions of a political tweet make it more likely for it to be used by a journalist and to which extent the journalist’s Twitter network plays a role in this process. We analyze which functions of political tweets explain their use as information subsidies and integrate the influence of the journalists’ Twitter networks. The study is based on a unique combination of an online survey of Swiss journalists in 2014 with an analysis of the journalists’ Twitter metrics. It demonstrates that political tweets are most likely to be used by journalists if they can quote the politicians’ tweets, which fosters their significance as information subsidies. Also, journalists who have many politicians as followers perceive that they can influence politicians they do not know personally. This underscores that if the Twitter network is included in the analysis of agenda-building processes, potential reciprocal influences can be detected.