Hello,
I suggest you to use Google Adwords alongside Social Media to promote your App. Often AdWords gives even better results. But it depends on the app promoted. I have experience in promoting different kind of apps from dating (HiHi, Badoo, Love Planet) to E-commerce (AliExpress) in google and facebook, so anyway I can help you with yours. What kind of app do you want to promote?
Feel free to contact me anytime!
Best regards,
Aleksandr Mishurov