Sorry, I don't really understand what you're asking? - transistors don't "amplify current".
In this circuit they are simple switches - they switch the bottom end of the LED down to 0V, that's all you need to know really.
However, it's a really poor circuit, the regulator is missing at least one essential capacitor, and there's no HT decoupling capacitor on the multivibrator either. Also, the supply of 12V is too high for most transistors, and the transistors will very quickly fail.