Background Although social support has been consistently associated with recovery from psychological trauma and prevention of posttraumatic stress disorder (PTSD), individual differences in seeking or benefitting from social support in trauma survivors are not well understood. Factors associated with negative internal working models of self and others, emotion dysregulation, and interrupted bonds with an individual’s social support groups such as vulnerable attachment and rejection sensitivity could contribute to lower experienced social support and higher levels of PTSD. Objective The objective of this study was to test a theoretically informed model and investigate how psychosocial variables such as vulnerable attachment styles, rejection sensitivity, and social support are associated with PTSD. Method Using a cross-sectional survey and path analyses in 141 survivors of trauma (aged 18–69, M = 25.20), the relationship between vulnerable attachment style, rejection sensitivity, and PTSD were investigated. Results Higher vulnerable attachment, rejection sensitivity, and lower social support were found to be significant predictors of PTSD symptoms ( f 2 = 0.75). The relationships from vulnerable attachment to PTSD were mediated by rejection sensitivity and perceived social support. The results supported and extend theoretical models of PTSD that posit a role for predisposing factors in the development and maintenance of the disorder. Conclusion The findings suggest a potential benefit of identifying vulnerable groups that could benefit from a refinement of existing PTSD interventions by targeting the maladaptive effects of vulnerable attachment and rejection sensitivity, thus allowing the individual to draw effectively on social support networks.