I am the only one who sees a resemblance between this film and Avanti?

In a way these are very different movies: Billy Wilder's is a comedy whereas 'Missing' is a political thriller, but in closer inspection they have a few remarkables similarities:

Both have Jack Lemmon in the leading role and in both he plays similar characters: a kind of uptight businessman type, a sort of "ugly american" traveling foreign country and in both films his characters evolves and changes along similar lines, becoming a very different person in the end.