Marketing company to help market new app

Hello I am 3 weeks out to launching my new app similar to candy crush I am looking for a company to help me set up marketing for this I am 100% brand new to this don't know if I will need Facebook Instagram or what else I would need to market the app Succeed in the Apple store and Google play store Please have a full detailed plan on how you plan to help me take my app to the top of the charts Looking for a company I can have a long relationship with