As long as you are logged in and have a published ad you will see a text entry messaging window at the bottom of all house sitters public profile page. If there isn't one it may be because you don't have a published ad. If you don't, at the bottom of all sitters public profiles, under the heading 'Contact Sitter' it says "To be able to contact this House Sitter you need to have a current published ad. Please click this button:"