Luna Display's Target Display Mode Feature Adds Ethernet, Thunderbolt - The Mac Observer
Luna Display's powerful Target Display Mode feature for Mac adds Ethernet and Thunderbolt support - 9to5Mac
Amazon.com: Cable Matters 4K Mini DisplayPort to Mini DisplayPort Cable in Black 3 Feet - Not a Replacement for Thunderbolt Cable, Not Compatible with iMac, Not Support Target Display Mode : Electronics
iMac won't enter Target Display Mode - Apple Community
Instructions: Use the iMac as a Windows PC monitor »Sir Apfelot
Target Display Mode with an iMac - Promise Pegasus R6 & Mac Thunderbolt Review