app/views/spree/social/_tumblr.html.erb
<% title = Spree.t(:share_on_tumblr, scope: [:social, :buttons]) %>
<%= link_to 'http://www.tumblr.com/share/link?' + { url: spree.product_url(@product), name: @product.name, description: @product.description }.to_param, title: title, class: 'tumblr-share' do %>
<%= title %>
<% end %>
<script src="//platform.tumblr.com/v1/share.js"></script>