Following article describes how to restore this functionality.
1. Download SDK for Dynamics CRM 2013 using following link - http://www.microsoft.com/en-us/download/details.aspx?id=40321
2. Unpack it to your hard drive and open
3. Import solution DuplicateDetectionSample_1_0_0_0_managed.zip to your CRM:
Here are parameters that have to be passed to onsave event handler:
false, "contact", "contactid", ["fullname", "firstname", "lastname","emailaddress1"], "sample_/duplicateDetection/ShowDuplicateContacts.html", "dialogHeight: 250px; dialogWidth: 600px; resizable: yes; status: no;"
6. Open new contact form and try to create contact that would be potential duplicate. If you have done everything in a right way you will see following popup:
Full documentation and installation instructions are located in