This study examines the individuals' participation intentions and behaviour on Social Networking Sites. For this purpose, the Decomposed Theory of Planned Behaviour is utilized. Data collected from a survey of 1100 participants and distilled to 657 usable sets has been analysed to assess the predictive power of Decomposed Theory of Planned Behaviour' model via structural equation modelling. The results show that attitude and subjective norm have significant effect on the participation intention of adopters. Further, the results show that participation intention has significant effect on participation behaviour. However, the study findings also show that perceived behavioural control has no significant effect on participation intention or behaviour of adopters. The model adopted in this study explains 47% of the variance in "Participation Intentions" and 36% of the variance in "Participation Behaviour". Participation of behavioural intention in the model' explanatory power was the highest amongst the constructs (able to explain 14.6% of usage behaviour). While, "attitude" explain around 9% of SNSs usage behaviour.