Here's how to launch search results in your Spotify desktop app from the address bar of your web browser:
To get Eminem:
To get Foo Fighters:
To make this work from Launch Center Pro on your iOS device, create a new action and put this in the Action Composer:
When you launch the action, just enter your musician or band in the prompt (without the + between words), and LCP will open Spotify to the search results for that query.