A higher quantity and quality of social relationships is reliably linked to improved mental health. However, little is known about how individuals effectively cultivate these beneficial social networks. We explored this question in four real-world social networks and investigated whether individual differences in empathy and prosociality shape social network structure. Across all four networks, individuals who reported higher levels of empathy and prosociality maintained more social ties that were reciprocal and were more frequently nominated as a source of social support and positivity by other network members. Thus, empathetic and helpful individuals may develop a broader social network by consistently boosting others’ positive affect. Interestingly, individuals that the social network identified as empathetic and prosocial reported greater happiness and less loneliness, suggesting that meaningfully engaging with network members may promote one’s own positive affect and well-being. These findings demonstrate the central role of empathy in spreading positive emotion and well-being across social networks.