I just learned about this app, Mine, that allows you to connect your Google or Microsoft email account and discover who around the Web has your data.

By signing in with your email, it allows us to scan the subject lines and metadata of your emails (we never collect or store this information) to find those traces and reflect them back to you. 

It also offers some quick options for closing old accounts and requesting companies delete your personal information. 

Check it out at www.saymine.com.