For tracking social media posts that take your visitors to your Marketo landing page, if you use Hootsuite, you can track the clicks for Facebook, LinkedIn and Twitter posts, if that's what you use, but you have to set up the analytics there. It's easy. But if it's just Twitter, you go to your account, click on the Advertiser link, logon with your username and password, and then you'll see the timeline analytics for the clicks on the upper left hand side.
And I do what Jeff mentioned above for website tracking.