Background: Social communication skills are critical for full participation in social activities in primary life contexts for adolescents and young adults with neurodevelopmental disorders. Method: Two young adults with Prader Willi syndrome participated in an online socialisation programme with elderly and adolescent conversational partners. We used a multiple baseline across conversational partners design for each participant to investigate the effects of textual prompts and constant time delay on the number of initiations and follow-up questions. We evaluated the social validity. Results: Both participants improved their social communication skills during online socialisation with partners. Participants with Prader Willi syndrome enjoyed participating in this study. Elderly conversational partners reported a slight decrease in loneliness following online socialisation. Conclusion: The use of textual prompts and constant time delay may be helpful to promote opportunities for interaction among segments of the population potentially at risk of social isolation during online socialisation.