(Update: JXcore extension in Plesk has been deprecated and no longer available. Plesk provides new extension for Nodejs and Docker.
I wrote update: "How to Install Ghost with Node.js Extension in Plesk Onyx").
Installing Ghost in Plesk 12 panel is easy, just install JXcore Plesk for Node extension and ready.
1) Install JXcore Plesk for Node from menu: Extensions > Extensions Catalogs > Install JXcore Plesk for Node
2) Click JXcore Plesk for Node and activate the option "Allow user to install NPM module" and clik OK:
3) Copy Ghost files to root of web folder: /var/www/domain.com/httpdocs or some other folder you defined for root of web files.
4) Write NODE_ENV=production in "Environment variables":
5) Finish, Ghost now active with Plesk panel.