Facebook on mobile is fantastic– it’s about half of their traffic. But you don’t need to build a mobile app to get mobile traffic.
Your page’s newsfeed is already designed to work on mobile.
And your ads should work on mobile. No touch is needed from you.
If you do mobile anything, just make sure your website is mobile-friendly/responsive.
And you may build an iTunes app or Google Play app if you’re a major brand with an interactive app that does something.
Canvas and tab apps largely died two years ago, although you can still run some contests and landing pages if you amplify them with ads.
Focus on content and content amplification if you’re a small business or don’t have a large dev team.
Don’t build an app just because you think it’s cool. Create real value for your customers.