Search for tapatalk on these forums. For a standard xenforo forum, tapatalk would work. If you have any addons, they would not be translated well into the tapatalk mobile app. There has been a lot of discussion on this topic already, ranging from tapatalk and how it hurts your adsense revenue, to them bypassing the xenforo standard registration and spammers entering the site through that.
I have tried tapatalk. Will never go back to that or make my site reliant on a 3rd party. Its a germ that needs to be killed.