The rapid growth and influence of social network services has led many scholars to focus on privacy issues. However, the research described in this thesis was motivated by the small number of design studies that have focused on practical approaches to identifying tacit information from users’ instant non-verbal responses to privacy issues. The research therefore aimed to propose persona models as a design solution for software agent development based on the analysis of users’ emotional and behavioural responses, so as to address privacy issues in social network services. In the definition phase, 21 stakeholders belonging to three key stakeholder groups were recruited for unstandardised semistructured email interviews. Three main considerations for the design of software agents in social network services emerged from the interviews, which were classified into the following categories: comprehensive understanding of users’ perceptions of privacy; user type recognition algorithm for software agent development; and existing software agent enhancement. In the development phase, 50 participants were recruited for the Facebook case study, which included three research strategies: perceptions of privacy questionnaire for user typology; emotional response measurement using Geneva Emotion Wheel; and behavioural response observation using a contextual inquiry method. The participants were classified into four user types by means of cluster analysis: uninformed, trustful, suspicious and neglectful. Each user type’s key emotional responses were identified using Kruskal-Wallis test and Mann-Whitney U test, and key behavioural responses using affinity diagrams. This generated persona models of each user type that reflected the correlations between users’ perceptions of privacy, key emotional responses and key behavioural responses. Two fundamental features of the software agent were also proposed based on the persona models: confirmation and guidance. In the validation phase, software agent prototypes were created based on the proposed persona models. A total of 206 participants completed the online survey which included two sections: perceptions of privacy questionnaire for user typology replication, and key emotional responses measurement before and after the intervention of the software agent prototypes. Cluster analysis replication validated the proposed user typology, and Wilcoxon signed-rank test of key emotional responses validated the proposed persona models. By implementing the research outcomes, the software agent described in this thesis would be able to provide users with appropriate services based on their user types, to reduce the number of those who are still unaware of privacy practice and those who neglect their accounts, and to expand the size of a user group pursuing sound relationships.

The number of social media platforms (SMP hereinafter) is ever-increasing, and all of these platforms compete for more attention and content. The global social media market is expected to grow to $223.11 billion in 2022 (Social Media Global Market Report, 2022). In an era characterized by the meteoric rise and evolution of Social Media Platforms (SMPs), understanding the interplay between platform features and user behaviors is both critical and complex. In this dissertation, we aim to elucidate the relationship between SMPs and society, with the ultimate objective of fostering a healthier social media ecosystem. This dissertation is comprised of two incisive essays, both of which are underpinned by robust theoretical frameworks. The first essay adopts an expansive purview of the SMP ecosystem. Grounded in Uses and Gratifications Theory and media studies, it establishes a user typology based on the previous typologies and examines the interaction between user motives, SMP scores, and SMP features. Employing the Analytic Hierarchy Process, a sophisticated decision-making tool, the study quantifies utility-driven choices across platforms. A notable revelation is the heterogeneity in user reliance on SMP features, contingent upon their underlying motives. This essay offers critical insights into the multifaceted nature of SMP utilization. The second essay focuses specifically on Reddit's ChangeMyView community, an exemplar of constructive discourse in the SMP environment. It constructs a theoretical model premised on the Elaboration Likelihood Model and the concept of pre-suasion, and utilizes a mixed-methods approach to explore the persuasive strategies using Content Analysis. We also utilize ChatGPT in the Content Analysis to corroborate our inferences. The findings confirm our theorization about the role of the Delta reward system in fostering reflective engagement with content, which leads to informed opinion formation. Collectively, with these essays, we aim to provide extensive insights into the dynamic interplay between SMPs and users. Both essays hold significant implications for research community, SMP decision-makers, organizations that use SMPs, and a broader audience interested in optimizing their social media repertoire. Through a theory-driven and empirical lens, employing several epistemologies, this dissertation provides a holistic depiction of the SMP ecosystem. / Doctor of Philosophy / The landscape of social media is constantly evolving with an ever-growing number of platforms vying for user attention. In this dissertation, we aim to analyze the relationship between social media platforms and their users, seeking ways to foster a healthier and more constructive social media environment. This dissertation is structured into two distinct yet interconnected essays. In the first essay, we look at the broader ecosystem of social media platforms. It categorizes users based on their motivations for using social media, such as seeking information or connecting with others. We examine how different features of social media platforms cater to these diverse motivations. To accomplish this, we employ a method known as the Analytic Hierarchy Process, which is a decision-making tool used to measure and analyze choices. The key insight from this essay is the diversity in how users interact with social media features, and how this interaction is influenced by their underlying motivations. In the second essay, we take a closer look at a specific community on Reddit called ChangeMyView. This community is unique as it encourages users to engage in thoughtful and reasoned debates. In this essay, we develop a theoretical model to understand the mechanisms through which information is processed and opinions are changed within this community with a strong focus on Delta system, a feature that rewards users for successfully changing someone's opinion through challenging their view and pointing the flaws in their thinking. Collectively, the dissertation provides an in-depth understanding of the dynamic relationship between social media platforms and users. It does so through rigorous analysis underpinned by theoretical frameworks. This research is not only academically significant but also has practical implications. It provides valuable insights for decision-makers to improve social media platforms, aids organizations in understanding how best to engage with social media, and informs users on optimizing their social media interactions. In essence, this dissertation serves as a comprehensive analysis that bridges the gap between the ever-evolving features of social media platforms and the multifaceted behaviors of their users.

Die Arbeit beschäftigt sich mit der Frage, welche Motive Konsumenten dazu verleiten, soziale Medien im sogenannten "Web 2.0" aktiv oder passiv zu nutzen. Hierbei liegt das Augenmerk insbesondere auf soziodemographischen und psychologischen Merkmalen der Nutzer. Als zentrales Ergebnis der Arbeit kann herausgestellt werden, dass sich die befragten 188 Personen insgesamt anhand von zwei Dimensionen: Aktivität vs. Passivität und soziale Motivation vs. individuelle Motivation in 5 Gruppen beschreiben lassen. Mithilfe klassischer und neuer Marketing-Instrumente (z.B. Virales Marketing) lassen sich diese Gruppen zielgenau ansprechen.

Die Arbeit beschäftigt sich mit der Frage, welche Motive Konsumenten dazu verleiten, soziale Medien im sogenannten "Web 2.0" aktiv oder passiv zu nutzen. Hierbei liegt das Augenmerk insbesondere auf soziodemographischen und psychologischen Merkmalen der Nutzer. Als zentrales Ergebnis der Arbeit kann herausgestellt werden, dass sich die befragten 188 Personen insgesamt anhand von zwei Dimensionen: Aktivität vs. Passivität und soziale Motivation vs. individuelle Motivation in 5 Gruppen beschreiben lassen. Mithilfe klassischer und neuer Marketing-Instrumente (z.B. Virales Marketing) lassen sich diese Gruppen zielgenau ansprechen.