The Hollywood Reporter has posted that Michael Bay has begun testing various Hollywood young actors for the role of Mark Wahlberg's daughter and her race car driver boyfriend leads for Transformers 4. Basically Bay is going for virtual unknowns that have some acting experience but the average movie goer probably would not recognize (pretty much like how he cast the previous three films).
For the female role Isabelle Cornish (Australia's Home and Away), Nicola Peltz (Avatar: The Last Airbender), Margaret Qualley, and Gabriella Wilde (Carrie, Three Muskateers) are currently testing.
For the boyfriend its Luke Grimes (Brothers & Sisters, Taken 2), Landon Liboiron (Terra Nova), Brenton Thwaites (Blue Lagoon), Jack Reynor (beats me) and Hunter Parrish (Weeds).
This group is likely to change as this is just some of the many actors Bay is likely checking out. Of this small group I am partial to Nicola Peltz due to potential shown in Avatar and she has green screen experience the others don't really have. Based on the pic of her with Mark at last year's season premiere of Boardwalk Empire, they look like could easily sell being father and daughter. Considering every TF film had a long haired blonde personally selected by Bay, Gabriella probably has a leg up here. On the male side Jack Reynor pops the most for me. Any case probably be a few months before anything official is announced.