Last week I posted a 
story that Peter Jackson was heading right in to 
The Adventures of Tintin sequel right after filming 
The Hobbit using 
The Seven Crystal Balls and 
Prisoners Of The Sun as the story. Sequel writer Anthony Horowitz said down with 
BBC, Via 
Bleeding Cool, and denied that he is using Prisoners of The Sun for the second movie.
Said Horowitz:
"I can tell you that I think the second film is not going to be Prisoners of the Sun. What it is going to be is still under discussion. I’ve had meetings with the directors and producers and we’ve talked about ideas and action sequences. At the moment I’m trying to put together a story that will please everybody. It’s a very difficult one to do.
But if you were hoping to see that story developed into a Tintin movie fear not. Horowitz also said that 
Prisoners of The Sun will likely be for a third Tintin film. Saying, 
"The good news is if [Prisoners Of The Sun] is not the second film it'll be the third film so actually I could end up with two Tintins under my belt."
This makes sense because 
The Prisoners of The Sun is suppose to take place after 
The Seven Crystal Balls, so if they are going to do a third film it would make sense that 
Prisoners of The Sun would be the story for it.