These images were posted in the above thread purportedly from 777 maintenance manuals. The diagrams bear a very good resemblance to the photos thus far:
http://i.imgur.com/OAw6AOc.jpg http://i.imgur.com/Ti09xEh.jpg
http://i.imgur.com/OAw6AOc.jpg http://i.imgur.com/Ti09xEh.jpg
On the other hand, it's pretty rare for large aircraft (or large parts thereof) to go missing, so there aren't a whole lot of places from which this piece of wing could have come.