The first Tin Tin was a pretty big hit when global box office is considered, so they are definitely moving forward with the sequel. As originally planned, Spielberg directed the first one and Peter Jackson will direct the second. Spielberg recently mentioned the project while talking to the India Times.

On when we can expect to see it:

“Peter Jackson is directing the next one, I’m producing. We have a script and we’re going to start performance capture probably at the end of this year. Don’t hold me to it, but we’re hoping the film will come out around Christmas-time in 2015. We know which books we’re making, we can’t share that now but we’re combining two books which were always intended to be combined by Herge.

On the story:
“We have finalized a script for a movie that DreamWorks (the studio he co-owns) and our partners Reliance Entertainment plan to make together. Part of it will take place on the India-Pakistan border in Kashmir. But we’re still trying to figure out the casting, locations and who’s going to direct it.”

Source: Collider