When you see a poinsettia runner on Pintrest that you like, are you clicking on the "Visit" button? Sometimes the blog it leads you to will feature the pattern.
Better yet, I found luck when I actually search Pinterest (or google) the words "Poinsettia table runner pattern.' You need the word "pattern" in there or else you might get only images. If you want a free pattern, include the word "free" in your search.