I'm an alliance leader and my alliance store is empty what should I do?

Go to the alliance store and tap the 'Item List' tab at the top. In this section you can buy items to put in the store for the other members to then buy and use. You buy the items with 'Alliance score' points. The items are then transferred to the store. You and others then buy them with 'Alliance contribution' points.

If you don't have alliance score / contribution points then your alliance members need to do a lot more donating.