Rails: Open link in new tab (with ‘link_to’)

The target: :_blank parameter should be a parameter of link_to, whereas you put it in image_tag parameters. Modify your code like this:

<%= link_to image_tag("facebook.png", class: :facebook_icon, alt: "Facebook"), "http://www.facebook.com/mypage", target: :_blank %>

Or with a block:

<%= link_to "http://www.facebook.com/mypage", target: :_blank do %>
  <%= image_tag("facebook.png", class: :facebook_icon, alt: "Facebook") %>     
<% end %>