His mom and dad divorced when he was a little baby and his dad went out of town, working, and kind of abandoned Justin, and Justin was/is very emotional about it :)
I think the song is saying someone in his life is mad at him and wont speak to him but he needs them more than ever now. It could also be that he has done something wrong and he needs forgiveness but...
If You Thought It Was About His Dad Your Wrong. He Says "Me And My Dad See Eachother All The Time Get Your Facts Straight" To People Who Asked About His Song It About A Past Relathionship.
Intro: Am F G Am F GAm F Where are you now Am F When I need you the most Am F Why don't you take my hand G I want to be close Am F G Take my hand and walk with me, yeah Am F Where are you now Am F...