An increasing number of middle-aged and older Americans are using social network sites (SNSs), but little research has addressed how SNS use is associated with social wellbeing outcomes in this population. Using a nationally representative sample of 1,620 Americans older than 50 from the 2012 Health and Retirement Study (HRS), we examine the relationship between older adults' SNS use and social wellbeing associated with non-kin and kin relations and explore how these associations vary by age. Results of ordinary least-squares regression analyses suggest that SNS use is positively associated with non-kin-related social wellbeing outcomes, including perceived support from friends (β = 0.13; p < 0.001; N = 460) and feelings of connectedness (β = 0.10; p < 0.001; N = 463). Regression models employing interaction terms of age and SNS use further reveal that SNS use contributes to feelings of connectedness to a greater extent as people age (β = 0.10; p < 0.001; N = 463). Of all kin-related social wellbeing outcomes, SNS use only predicts increased perceived support from children (β = 0.08; p < 0.05; N = 410), and age negatively shapes this relationship (β = -0.14; p < 0.001; N = 410). As older people engage with an increasingly smaller and narrower network with a greater proportion of kin contacts, our results suggest that SNS use may help older adults access differential social benefits throughout later life.