If you signed up for a Pinterest account using your email address, your Pinterest profile was not linked with your Facebook account. Although you can link the two accounts from the Account Settings page at any time, Pinterest does not post your pins on your Timeline by default. You need to enable this functionality from the same Account Settings page after you link the accounts. Once enabled, Pinterest posts all your pins on your Timeline without notifying you.
Click your name after you log in to Pinterest and choose "Settings" from the menu to open the Account Settings page.
Click the "Log in with Facebook" switch in the Social Networks section and then log in to your Facebook account in the new Web browser window that displays.
Click "Okay" to allow the Pinterest app to access your Facebook information. You can't link the accounts if you click "Cancel."
Click "Okay" to allow the Pinterest app to post on your Facebook Timeline. The new browser window closes automatically.
Click the "Link to Timeline" switch in your Pinterest browser window to allow the Pinterest app to post your activity on your Timeline.
Click the "Save Settings" button to save and apply the new settings. Pinterest posts all your new pins on your Timeline immediately.
You can link Pinterest to your Twitter profile from the Account Settings page by clicking the "Log in with Twitter" switch.
To unlink Pinterest from Facebook, click the "Log in with Facebook" switch.
If you want to erase all Pinterest activity from your Timeline, check the "Delete all your Pinterest activity on Facebook" box when you remove the app from the App Settings page on Facebook.