The Invoicing module on AccountancyManagers has a feature for viewing all of your debtors. You can use this to keep up with unpaid invoices and client debt. To access it, go to Invoicing > Debtors.
The Debtors list will appear. Here you can see all your Debtors, and download a statement to send to them. There is a search option in the top right to find specific items and sort buttons available on many of the headers.