Why doesn't my 555 + MOSFET setup drive my motor?
I bet you will learn a lot more if you figure it out yourself.  

So, rather than telling you the answer, I am going to help you to get the answer yourself.  

First break the problem/circuit into parts and check each part against how you think it should work.  

I recommend:   


555 and RC
BJT
FET
Motor


For each part, consider what is required for each state.  Start at the Motor and work backwards and check each with a DVM until something doesn't respond as you expect it would.

Ex: For the FET   

Input(G)     Output(D)   Result   
0V           Off (3V)    Motor Not Running   
9V           On (0V)     Motor Running