Thanks everyone! I changed my fb settings to where only friends may message me. If the person continues to ask me, using other means, I will use FoxPaws's suggestion.
Pierrotlunaire0, knowing friend, you are probably right.
Shoo, friend and I were friends in real life. I found a fun site and invited friend to join. The group knew that we would often be on the phone with each other while chatting to everyone else.