How do you say good evening mom in french?

Bonsoir, mon ami(e)

*Bonsoir is the correct translation of good evening, but for "friend" you would say Bonsoir, mon ami (male) or Bonsoir, mon amie (female) The plural would be Bonsoir, mes amis.

Alternatively, if you wanted to say "have a good evening" as a farewell, you would simply say Bonne soirée.