In Nishmat Avraham vol. 4 pg. 207 Rav Avraham Steinberg quotes Rav Shlomo Zalman Auerbach, Rav Eliashiv and the Tzitz Eliezer as saying htat a molester is a rodef and it is permissible (and presumably a mitzva) to report him.Rav Menashe Klein (Mishna Halacha 16:8) says that if the person will leave education (in the case of a teacher) such that that he will no longer commit these acts it is sufficient. If not, his name should be publicized. He also requires “proper witnesses”, which is very difficult to understand (see Choshen Mishpat 2:1 with Rema).
Of course, one must be certain that there are “raglayim ladavar” and it is not an attempt to “get” somebody or the result of an overly active imagination. This is also the position of the Agudath Israel of America (in its clarification of its postition).