A Specific Approach
The causal mechanism that may connect X and Y can be analyzed by looking at the amount of political advocacy groups currently on facebook or Twitter dealing with current events that promote or discuss political activism. We would then have to figure out what influence these pages have had on the general public. This is where our survey questions could become very effective if we for example asked things like "Do you affilitate yourself with a political advocacy group on social network sites or How often do you recieve updates on events which would involve your advocacy for a particular global issue..."
There is a definate possibility that there may be a confounding Z variable but then we can shift the focus of our topic and instead determine whether social media sites have facilitated political activism.