I've begun seeing posts (and comments) telling you how to get free PokeCoin. Let me be clear here and now…
THIS IS A SCAM
The only ones who can give you PokeCoin is Niantic and they don't need to run any promotions. And since PokeCoin cost real money, nobody is going to give them away.
The only way you could get them for "free" is by earning Google Play credits via Google Opinion Rewards https://goo.gl/HVMGni where you take the occasional survey, earn uoto $1 in store credit and use that to buy PokeCoin. (like I did)
Unfortunately, Google Opinion Rewards will not earn you credit quickly since most surveys earn 10-20 cents and can take a few days between surveys.