Making it noticeable

It's a bad approach to make the user look for the search box. The search box should always be easy to find, especially when you have a lot of content on your website. Make your search bar stand out by using contrast or color. It's also important to display a full open-text field because a search bar hidden behind an icon makes the search feature less noticeable and increases the number of clicks to access it: 

Here's what the Amazon website for mobile looks like: 

You can see here that Amazon focuses on this search bar on mobile and doesn't hide it.