I solved the problem, so I am adding this as answer.
I mixed up with bundle identifier and product identifier. My code was correct, I provided bundle identifier instead of product identifier, this is the reason that I was not getting any products.
NSSet *productIdentifiers = [NSSet
setWithObjects:product_identifier,nil];
productsRequest = [[SKProductsRequest alloc] initWithProductIdentifiers:productIdentifiers];
In the above code use product_identifier(s). as I've only one product created so I am using single element to construct the set.