This is an extension supported for VS2010 and VS2012. It searches and highlights all occurrences of a selected word in a text editor.
For VS2013 and VS2015 support, reference to https://marketplace.visualstudio.com/items?itemName=TrungKienPhan.WordHighlight-18643
For VS2017 support, reference to https://marketplace.visualstudio.com/items?itemName=TrungKienPhan.WordHighlight-18439
Install the extension and verified that it is enabled in the Tools->Extension Manager.
In the editor window, when you select a word with a mouse or keyboard, this extension will searches and highlights all occurrences of current selected word in the current document.
You can change settings of the extension by go to "Tools" -> "Word Highlight settings..." menu.