Brazilians love the expression "Graças a Deus", and usually, when speaking english, make a silly mistake by saying "Thanks God" instead of "Thank God".
“Thank God” is actually a shortened version of “Thanks be to God” which means that you are telling the others (your friends or whoever) that you are thankful to God.
“Thank God” = “Praise God”.
But...
In case you are praying or directly TALKING to God, then you would say: “Thanks, God, for the amazing job I have” or "Thanks, God, for my beautiful kids", for example.
“Thanks” is an INFORMAL way of saying “Thank You”, so “Thanks, God” should actually mean “Thank You, God” if he was in front of you!
So, if you mean "Graças a Deus", the correct way of saying it is "Thank God".
