A person is a person. Refer to the individual as such.
1) If anybody asked you about the money, tell the person that it is in my bank account.
2) I felt that somebody was in the garden but I did not see anyone.
3) Speaker 1: A friend of mine helped me a lot.
Speaker 2: You should thank that friend / buddy / comrade / confidant.
4) Congratulations on your new baby! What's the baby's / child's / infant's name?