I've been playing this game for a while but on a guest account. I want to bind my Facebook account..

that is not true.. i lost everything on my old acc but i created a new acc then i logged in with facebook .. my old acc was back.. and I didn't even bound it …..

You know the scroll thing where are the events, achievements and all that? Scroll down and click on the link haired Nikki that said bond account

This is late, but for anyone else who has this problem, download the facebook app onto the device that you use love nikki. Then try again. This should work, it did for me.

You can't unfortunately. You need to start a new game from zero as a facebook user.