Laravel 5.1 custom 404 based on route

I'm new to laravel. I want to display a custom 404 error depending on requested url.

Example:
site.com/somepage
and
http://ift.tt/1VNjLKq

I've see this answer but it's for laravel 4. I can't find the equivalent answer for Laravel 5.1

Please help. Thanks!

via Chebli Mohamed