Drive LED strip from single LED
IN general you need a current sense amplifier or current mirror with gain ... which could be 1 BJT and 1 FET with R's for each. It could be highside sense differential V-controlled output current on the low side output , which needs 2 BJT's. 

But specifics depend exactly on your V or I input and V &amp; I output.   RGB strings may be 12V or single with 5V using Rs drops from V+ and regulated with PWM on the (-) input so there is no ground except at the driver.

More details needed.