Hey @Maci91 ,
Marketo has quite a few native integrations that you can set up to track paid/social media engagement.
Adwords:
https://docs.marketo.com/display/public/DOCS/Add+Google+AdWords+as+a+Launchpoint+Service+with+a+Manager+Account
https://docs.marketo.com/display/public/DOCS/Set+Google+AdWords+Conversions+in+the+Revenue+Model+with+a+Manager+Account
https://support.google.com/google-ads/answer/3073556
You may also want to look ingot the GA integration with Marketo:
demandlab.com/insights/blog/the-ultimate-google-analytics-and-marketo-integration-guide/
Facebook: https://docs.marketo.com/display/public/DOCS/Set+Up+Facebook+Lead+Ads
LinkedIn: https://docs.marketo.com/display/public/DOCS/Set+Up+LinkedIn+Lead+Gen+Forms
Additionally if you are pulling in UTM parameters from your tagged URL's into Marketo (hidden fields on forms or from querystring) you can use those as additional tracking parameters. IE visited web page with querystring xxx or with specific UTM values, or filled out form with specific UTM values for your known Marketo users. You may also want to look into storing UTM values in cookies, so if the user left the page and came back, your ad program would still get credit for the form fill. wiki.overstack.io/attribution/utm-capturing/
Thanks,
Megan