I have never tried it out myself but i expect you will get a response. But remember, they are extremely busy with filming Harry Potter and dealing with their personal lives so it may take a while for you to get a reply. You just have to be patient.

 

 

Also, you may wish to use their online form which is on their official website. Click on Fan Mail at the bottom of the site and fill out the form. You have to be a true JOP fan to use that form and they are scanned for foul language. If it contains bad language, it will not be sent :)