According to Microsoft support:
Visual Source Safe is no more is an active product and its no surprise
if the plugin is not available in Visual Studio 2013 as Microsoft
stopped supporting it long ago and its replaced by Team Foundation
Server. If you are still using Visual Source Safe, its recommended to
upgrade to Team Foundation Server.
You can use Team Foundation Server Express (up to 5 users) for free
and use the Visual SourceSafe Upgrade Tool to import your project
directly into TFS. Or buy a full server from $400 and up.
Alternatively, you can open a Visual Studio Online account (free for 5
users) and migrate your sources to the cloud. You can add additional
users for a monthly license fee.
If you are an MSDN subscriber or Microsoft Partner, your subscription
might actually include a full TFS license.
Source: https://social.msdn.microsoft.com/Forums/en-US/40136b63-96ab-4807-9599-ca80c3a7bb7a/how-to-open-visual-source-safe-in-visual-studio-2013-express?forum=tfsversioncontrol
Update : I've found that you have to install the VSS after VS2013 on your system. please reinstall it.