Great fun to be had here! What you need to do is write the Doctor a letter and await his reply, the person who posts after you has to do the reply and then ask a question of their own for example:

Poster ONE: dear doctor are you my mummy? Love Martha


Poster TWO: No, i am not your mummy, now GO TO YOUR ROOM!

Dear Doctor, what happens if i press this big shiny button marked DO NOT TOUCH?


does that make sense?

Okay i'll start.

Dear Doctor

Is it true that Rose once danced with you and Capt Jack at the SAME time?
love and respect
Curious Fan!