Firstly, if you don't have a track record of writing 'hits', then it's going to be extremely tough getting heard by any of the major players. Your song has to be absolutely knockout and so obviously a hit that people will take notice. Ask yourself honestly if this is the case. Seek impartial opinion from people you trust and are knowledgeable - not family and friends!!
If you're still convinced it has legs, then a focused and targeted approach is essential. Decide who it is suitable for and work backwards until you find someone who has the access you need ( manager, PR, legal etc).
Tip sheets may be worth a shot also. (Some have publishers who are accepting submissions and even decent label artist contacts).