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