i started to use plataformIO in Atom, for my arduino project and looks pretty amazing, but in the uggly Arduino IDE, i can put in the serial monitor an AT command and watch the answer. i wrote a simple code for use a ESP8266 from arduino uno, and when i check it work or not, i open the serial monitor and insert text, but nothing happen. How i use the serial monitor for this? 
Does it work when you type text manually within PlatformIO Serial Monitor?
I don’t understand your question. I followed this tutorial (only see the pictures, this is an Spanish tutorial) Como conectar Arduino a una red WIFi con el módulo ESP8266 | Leantec.ES with IDE arduino and works. Now i try to do the same in the atom with plataformio and the serial monitor don’t show anything. If i code something and upload to mi esp8266 through my arduino, that’s work.
Could you share here screenshot of PlatformIO IDE + Serial Monitor?