Director Michael Bay announced some casting news for the upcoming sequel "Transformers 4" via his blog site. Bay also gives a bit of information on the fourth film, saying it will not be a reboot and so on.
Here is what Bay said:
I just hired a great new actor for Transformers 4 to star against Mark Wahlberg. Jack Reynor, he is an Irish kid that came to America with 30 bucks in his pocket. Pretty ballsy. Seriously who does that? Anyway I spotted him in a great little Irish movie WHAT RICHARD DID. This kid is the real deal.
Transformers 4, is not a reboot. That word has been floating around on the net.
This movie takes place exactly 4 years after the war in Chicago. The story makes a very natural transition, and reason as to why we have a whole new cast. This Transformers will feel very different then the last three. We are embarking on a new trilogy.
Source: Michael Bay