Go to Tiddler:
<$edit-text tiddler="$:/temp/goto" tag="input" default=""/>
<$button to={{$:/temp/goto}}>Go</$button>
<% if [{$:/temp/goto}is[tiddler]] %>
  <span style="color:green;">Exists!</span>
<% else %>
  <span style="color: red;">Not found.</span>
<% endif %>