Officials are worried there could be as many as 20 victims.
Rajeev Sanhi, 35, of Cupertino was arrested Wednesday on suspicion of stalking minors.
The investigation began after a 14-year-old girl claimed Sanhi followed her home more than a dozen times and repeatedly offered her gifts.
Police say Sanhi has also been connected to several South Bay churches and applied to be a teacher and a nanny.
When they searched his home Wednesday, police say they recovered photo collages of several underage victims, leading them to believe there may be more than four.