This thesis deals with the question of which success factors apply to social media marketing. German start-up companies are examined for this purpose. The investigation is based on ten semi-structured expert interviews, which are evaluated using a qualitative content analysis. The results show that there are many success factors and that companies proceed differently in many areas when implementing social media marketing measures. Important success factors are a tailor-made, company-specific social media strategy with a clear formulation of goals, integration of social media marketing into the corporate strategy, openness to new social media trends, credibility and reputation, compliance with data protection, the correct handling of criticism, use of social media as a market research tool and a long-term social media strategy. However, the significance of the results should not be overestimated, since this is a qualitative study with a limited range and only examines individual cases. Further research on the success factors could be based on quantitative studies or group discussions in which experts or users or customers are interviewed. Another possibility is the qualitative examination of the user-generated content.