Hi Guys
Here is my Solution for this Achievement.
The lost Hollywood Star is located on the first Island in the lower right Corner.
The Location is around the Coordinates X: 620.3 - Y: 557.1
You see 2 People hanging on a Tree and left of this on the Beachground a Head (X: 620.7 - Y: 557.7). Go to the Head and hit the X Button.
Thats all for this Achievement
Regards