the radiator is leaking the coolant and found out there is a very very tiny crack on the side of the radiator, and it's the plastic part. I am wondering if I can use something to glue it or not?
Thanks!!

You could try using some type of epoxy to seal the crack. JB weld is usually good, but these solutions are only temporary and don't always work.

The radiator will probably continue to leak and would eventually need replacement. Trying to patch it up probably won't hold up for too long if it does at all.

But then again, its worth a shot, after all, you have nothing to lose.

Welllll, I would disagree with "you have nothing to loose". I have seen 2 cases where the radiator crack grew into a hole that overheated and killed engines. Yes, very expensive engines.

I would replace the radiator and the thermostat ASAP.