But what if you meet several friends?
In that situation, you would say:
Kia ora e hoa mā!
Hello frieinds!
This is another situation where a word can have several differenrt meanings. Mā can mean "white" or "clean", so kia ora e hoa mā could mean "hello white friends" or "hello clean friends", but in this situation, mā is used to indicate the plural - that there is more than one friend.
When my children were little they went to school and had a teacher who used to greet them by saying: Kia ora tamariki mā! Because all the children in the class were pākehā, I thought she was saying: "Hello white children!". But mā indicates the plural and means: "all you":
Kia ora tamariki mā!
Hello all you children!