Which of these two do you mean:
- Please don't write this on my wall: "Thank you for visiting my profile"
- Please don't write this on my wall. Thank you for visiting my profile.
In the first case 'this' is the quoted wish: "Thank you for visiting my profile". If so, you don't need to specify the prohibited text (as it will be the previous comment on your wall [Note for the digitally challenged: the context is presumably Facebook ]); you could just say 'Please don't write that on my wall.'
In the second case, 'this' refers to something they have already written, referred to in your text and/or known from the context.
But as it stands your text makes no sense.
Student or Learner