Here is the full list of all 21 Lost achievements.
Jigsaw puzzle completed
Click 20
Click 12
Click 13
Click 14
Click 15
Click 16
Click 17
Click 18
Click 19
Click 1
Click 2
Click 3
Click 4
Click 5
Click 6
Click 7
Click 8
Click 9
Click 10
Click 11