Pre-order Now uses your storefront search engine to find products.
Is the product you're trying to find live on your store? If not, Pre-order Now unfortunately won't be able to find it.
The workaround for this is to temporarily put the product live, find the product in Pre-order Now, create a pre-order setting for it then hide the product again.
If the product is live on your store, your store is not password protected and your product is still not appearing in search, please contact support, and we'll be happy to help.