cockroach
 

i was trying to kill a cockroach and it went into my laundry room and i cant find it and i havnt seen it come out

If you saw one, you most probably have many, many more. You should call an exterminator, lay down a border of roach powder (boron will not hurt people or pets), or try those Combat discs.

Get yourself some Roach Away. Any Wal-Mart, Lowes HD and hardware store, or Dollar store should have it.
It's a Dry Powder.
Remove any outlet and switch covers and puff some inside the boxes, put some along any wall to floor areas and under the washer and dryer.
It kills them by dehydrating them not by posioning them.
I'd also buy some bug bombs so if there living inside the washer or dryer it should kill them.
There simply is no such thing as "one roach".