'nuget' is not recognized but other nuget commands working

How do I know if NuGet is installed?

In Visual Studio, use the Help > About Microsoft Visual Studio command and look at the version displayed next to NuGet Package Manager. Alternatively, launch the Package Manager Console (Tools > NuGet Package Manager > Package Manager Console) and enter $host to see information about NuGet including the version.

How do you set the local path of NuGet EXE to your path environment variable?

Click “Advanced System Settings” then click the “Environment Variables” button located within the Advanced tab. From here double-click the PATH variable in the top panel and create a new entry by adding the path to the directory that contains your NuGet.exe file (in this instance it's C:/NuGet/).

How do I force a NuGet package to install?

Switch to the Browse tab, search for the package name, select it, then select Install). For all packages, delete the package folder, then run nuget install . For a single package, delete the package folder and use nuget install <id> to reinstall the same one.

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:

Download NuGet.exe from https://github.com/NuGet/NuGet.Client/releases (give preference for the latest release);
Place NuGet.exe in C:\Program Files\NuGet\Visual Studio 2012 (or your VS version);
Add C:\Program Files\NuGet\Visual Studio 2012 (or your VS version) in PATH environment variable ~~(see http://www.itechtalk.com/thread3595.html as a How-to)~~ (instructions here).
Close and open Visual Studio.

Update

NuGet can be easily installed in your project using the following command:

Install-Package NuGet.CommandLine

In [Package Manager Console] try the below

Install-Package NuGet.CommandLine

There are much nicer ways to do it.

Install Nuget.Build package in you project that you want to pack. May need to close and re-open solution after install.
Install nuget via chocolatey - much nicer. Install chocolatey: https://chocolatey.org/, then run

cinst Nuget.CommandLine

in your command prompt. This will install nuget and setup environment paths, so nuget is always available.

You can also try setting the system variable path to the location of your nuget exe and restarting VS.

Open your system PATH variable and add the location of your nuget.exe (for me this is: C:\Program Files (x86)\NuGet\Visual Studio 2013)
Restart Visual Studio

I would have posted this as a comment to your answer @done_merson but I didn't have the required reputation to do that.

The nuget commandline tool does not come with the vsix file, it's a separate download

https://github.com/nuget/home

In Visual Studio:

Tools -> Nuget Package Manager -> Package Manager Console.

In PM:

Install-Package NuGet.CommandLine

Close Visual Studio and open it again.

Right-click on your project in solution explorer.
Select Manage NuGet Packages for Solution.
Search NuGet.CommandLine by Microsoft and Install it.
On complete installation, you will find a folder named packages in your project. Go to solution explorer and look for it.
Inside packages look for a folder named NuGet.CommandLine.3.5.0, here 3.5.0 is just version name your folder name will change accordingly.
Inside NuGet.CommandLine.3.5.0 look for a folder named tools.
Inside tools you will get your nuget.exe