Facebook has begun testing the option to geo-target Promoted Posts, even if the original post to fans was not geo-targeted. The targeting option was discovered by social marketer, Rich Tucker.
This additional geo-targeting feature may be helpful to marketers that have chosen to promote a post, but have not found success with the initial targeted audience. For example, if a marketer has chosen to target a precise area like San Francisco, they can also try to increase their reach by targeting a larger area such as California. It allows for marketers to adjust their strategies, barring disappointing results.
It also works in the opposite way as it allows for geo-targeting even if there had not been a specific geo-target selected initially. For example, a marketer may have chosen to promote a page post, but did not geo-target originally. When they select to promote it, they can now geo-target so that people in certain locations will see the promoted post.
Promoted Posts are page posts that get additional paid reach in News Feed among fans and friends of fans as a result of using a button on the page. Part of their appeal is that they don’t require page owners to create campaigns through the more complex ads create tool or Power Editor.
EDIT: It seems that Facebook has only begun testing this option for a select number of pages. It has yet to be rolled out to all pages.