Do you have some kind of written contract with the owner? Do you have detailed information on the inventory and costs of the items being held by the owner? If you do, notify the store owner (find out the name and address from the building lease owner) in a written document sent by certified mail that you want your items returned and if you don't receive them in a specified time, you'll sue in small claims court.
It might get a bit more tricky if you don't have any documents and the store owner owes money to the owner of the building--it that is the case, you might just have to throw yourself at the mercy of the building owner, as the owner will most likely keep the merchandise to offset monies owed by the shopkeeper.
In any case, get to the building owner ASAP to beat the rush.