Check out this very useful Chrome extension:
SlashSearch (or “slash search”) adds simple hotkey searching to any website. When you press the forward slash key on a webpage, it will do one of two things: 1. If the website has a search feature, SlashSearch will focus on the page’s search box. Just hit “/” and start typing your query! 2. If the website doesn’t have a search feature, SlashSearch will render its own search box. You can enter a query into the box and search the site using Google.