[mrverde]

On Facebook, there are granular privacy settings to control who can search for you by email/phone number if you choose to use them. They're accessed by going to facebook.com/settings (dropdown arrow @ top right), then "Privacy", then "Who can look me up?" ...the analogy would be opting to have an unlisted phone number in the white pages back when they were printed on paper and arrived on your front doorstep.