over heating and coolant loss

So ive replaced my thermostat and my fan is working, but somehow the car still overheats.i filled up the overflow tank today anf deove it for like 5 minutes and went inside and let the car sit and went back outside to check the coolant only to find coolant missing. What could be causing this? Theres no coolant in my oil. But I looked at the thermostat housing and on rhe aluminum crossover on the intake manifold there is like gunked up green, could this be coolant and why im overheating and loosing coolant. so im pretty sure it is leaking from the aluminum crossover where the gasket is right under the the thermostat housing. could this be my problem to my overheating issues? and if so do i need to get a new intake manifold. Thanks in advance for help

well it was orignally overheating so i replaced the thermostat and gasket, and it still over heats with a new thermostat. and today i only drove it for like 5 minutes and the temp gauge was just below half. i let the car sit for a while and then went and checked on it and the resivoir was between half way and a 1/4 way full. i put 2 gallons of coolant in it today before i drove it. and no exhaust smell