How do i turn a person in for distributing pills and serving alcohal to minors?

My son is 19 years old and lives at home with me. On our home phone i over heard my son talking to a girl, normal, except for it wasn'tt his girlfriend who he used to talk to every day. Well they are still together but we moved and she lives about 6 hours away, but she tries to drive down about 4 times a month. Well this girl he was talking to was selling him Narcotics and every time he visits this gas station in our town he comes home ( and thinks hes sneaking it) with bottles of alcohal and pills. This girl works for the gas station and needs to be stopped. My son wont admit it but i need to figure out how to get her fired or ticketed or somthing for how she is ruining my sons life.