Nuget.exe is placed at .nuget
folder of your project. It can't be executed directly in Package Manager Console, but is executed by Powershell commands because these commands build custom path for themselves.
My steps to solve are:
C:\Program Files\NuGet\Visual Studio 2012
(or your VS version);C:\Program Files\NuGet\Visual Studio 2012
(or your VS version) in PATH environment variable Update
NuGet can be easily installed in your project using the following command:
Install-Package NuGet.CommandLine