How do I replace the Xenforo Facebook recommend/like logo with my own?
Upload your logo to the server and change the image path in the ACP -> Styles -> Style Properties -> Header and Navigation -> Settings: Facebook Open Graph Logo. Due to caching it can take several weeks for the image to update on the Facebook servers.
It takes a while for fb to catch on. Sometimes weeks.
And then again, sometimes they don't catch on at all. I've seen my avatar, a forum button, etc up there. I've yet to see my logo.og image from my MVT site, even tho the logo.og image from my JRT site works every time.