"Grounding" somthing always involves a flow of current. We first have to learn how high thatcurrent is.
If it is - say - less 40mA the proposal from kg4 ist fine!
If it is higher you should in fact use a transistor. Please give us the diagram, so we can assess what went wrong the first time.
If it really has to be grounded, you most likely have to use a relay.