Unable to trigger NPN Transistor from 4017 decade counter output
Your schematic does not show symbols of LEDs. An LED is a diode, not a triangle.
Your first LED connects between the CD4017 output and the +12V supply so it lights when the signal is off (low) , not when it is on (high).

The LED connected to the transistor and through a resistor to +12V lights when the CD4017 output is on (high) only if the base resistor value is correct.

The datasheet of most little transistors shows that it turns on well (saturates) when the base current is 1/10th the collector current. the collector current in the 1k resistor is about 10mA so the base current should be 1mA. But your base current in the 470k resistor is only 0.000024mA which is way too low.

I agree that probably your LED was connected backwards at first which destroyed it.