Alexandra Potora said
1 year, 3 months ago: Hey @ianwilkinson, I hate to sound like a broken record, but you must be very careful with these types of contests, or you risk losing the pages. As @marylarson mentioned, FB functionalities as means of entering a contest or any monetary-giveaway are off-limits to Facebook. Here are their Promotions Guidelines just in case 
I haven’t had too much Good luck with any FREE apps. You can rarely go wrong with Wildfire or even Facebook sweepstakes though, if you want something cheap.
Good luck, let us know if you find something that fits your needs
~ Alexandra