After Twitchfilm.com reported last night that Nicola Peltz and Brenton Thwaites were confirmed to be cast in Transformers 4, Michaelbay.com responded with a post saying: "Actor announcement on some web sites last night about Transformer cast joining Mark are completely false."
Don't automatically assume it's false though for three reasons. One- Michael Bay did not say this, only an admin did. Two- When it was rumored that Mark Wahlberg joined the cast, Bay debunked it even though it ended up being true. Three- Twitchfilm.com is the same website that reported on Mark Wahlberg.
One thing I've learned about Michael Bay and his website is that they don't always tell the truth, so take this as a grain of salt for now.