Social networking sites (SNSs) are a ubiquitous phenomenon in today's society and their economic and social impact is high. However, despite the fact that many SNSs provide increasingly more system features to boost social networking, there is also an increasing concern about trust. Users' trust is important for a long-term oriented and successful SNS, based on a lively connecting behavior in SNSs. Nevertheless, so far only a limited number of studies investigated users' trust perceptions that are an important antecedent of connecting behavior in SNSs. We conducted a behavioral study, as well as a brain imaging experiment, to explore trustworthiness judgments in SNSs in order to better understand how pictures and textual information influence users' initial connecting behavior. Preliminary results of this research-in-progress paper show that both pictures and textual information have strong influence on trustworthiness judgments, and these judgments are processed differently in the users' brains.