The process of opinion formation through synthesis and contrast of different viewpoints has been the subject of many studies in economics and social sciences. Today, online social networks and social media have become the primary forum for people to create relationships, express opinions, and engage in discussions and debates. This has enabled the systematic analysis of opinion dynamics at a global scale, and has raised new research challenges. In our work, we adopt a well-established model for social opinion dynamics, and we study the following problems: (1) The Campaign problem, where the goal is to identify a set of target individuals whose positive opinion will maximize the overall positive opinion in the social network. (2) The Moderate problem, where the goal is to identify a set of target individuals whose moderate opinion will minimize the polarization in the network. In the course of our work, we uncover an interesting connection between the opinion formation process and random walks with absorbing nodes, and we propose a novel metric for measuring polarization in social networks.