Is there an book 4 in the missing series?

There is no book 4 in the "Missing" series. The series, written by Margaret Peterson Haddix, has only three books:

1. Missing (2002)

2. Found (2003)

3. See (2004)

The series follows the story of Jonah, a teenager who discovers he's a clone and must fight to save himself and other clones from the government.