There is a distinction between participants and observers; the former performs an activity, whereas the latter spectates. The idea of observers who can influence activities is largely unexplored and could contain potential use-cases for eye-trackers and improve social presence in digital settings. This thesis adds to existing research by investigating whether higher degrees of observer influence correspond to increased social presence perception in digital co-located settings. It also provides designers with a tool that helps design and evaluate interactions accounting for observers' influences. The thesis presents five gaze implementations across two games that allow observers to influence them to investigate the hypothesised link between social presence perception and an observer's degree of influence. The results indicate that the link exists, although more tests are necessary to determine whether there is a noticeable difference between observers who impact activities directly and indirectly.