Rails: Open link in new tab (with 'link_to')

Try this:

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

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 %>  

You can also use target: :_blank instead of target: '_blank'

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

link_to do

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