Contact the proper authorities. Any parish, diocesan office or local police station can hear your suspicions, help you evaluate the evidence you do have, and take appropriate action. If the priest has several other allegations against him, even if you do not have proof, another person voicing suspicions will call attention to the matter. Still, make real sure of your suspicions. Has the victim told you he or she has been abused? A false allegation can destroy people’s lives, both the life of the supposed perpetrator, in this case the priest, and also the suspected victim. No one, especially a child or adolescent, wants to be embroiled in the fantasy of someone’s overactive imagination, and have everyone in the parish or school thinking, “Oh, there’s the kid, so and so claimed Fr. “X” molested.”

Since 2002, the church has had a policy of zero tolerance. If anyone accuses a priest, he is immediately removed from ministry until the matter is resolved. Although false accusations are rare, priests are completely vulnerable to whoever wants to make a baseless claim. Priests must never engage in any kind of abuse. “When even a single act of sexual abuse by a priest or deacon is admitted or is established after an appropriate process in accord with canon law, the offending priest or deacon will be removed permanently from ecclesiastical ministry, not excluding dismissal from the clerical state, if the case so warrants.”

For more info check this link