IN BJT,
THE COLLECTOR CURRENT IS PRODUCT OF GAIN(β) AND BASE CURRENT.

AND β IS ALLWAYS GREATER THAN UNITY.

SO,THE CURRENT AMPLIFICATION TAKES PLACE ONLY WHEN INPUT SIGNAL CURRENT IS BASE CURRENT.
BUT WHEN WE CONSIDER CE CONFIGURATION,THE INPUT SIGNAL IS GIVEN BETWEEN EMITTER BASE TERMINAL,AND THE INPUT SIGNAL CURRENT IS EMITTER CURRENT,WHILE THE BASE CURRENT IS DUE TO REMAINING CHARGES WHICH HAVE NOT CROSSED THE BASE COLLECTOR JUNCTION,
THEN HOW CAN WE RELATE BASE CURRENT FOR AMPLIFICATION ?

 

You might find some useful knowledge in the transistor section in our Ebook - http://www.allaboutcircuits.com/vol_3/chpt_2/8.html.

In a common emitter setup, the signal does supply current into the base. The emitter handles both base and collector currents.