Is there a possibility to track visitors from other social media other than LinkedIn, FB and Twitter using social influence report.
How about Google+?
And how can we best integrate the existing social medias with Marketo.
Use UTM parameters.
Social Reporting in Marketo is really only about the prebuilt social connections within Marketo, which means you have to use it in a specific way, which I bet you don't.
Josh is spot on. I would highly recommend using UTM parameters, in my opinion they provide greater insight.