2D Vertical Shooter Joystick Setup

Hi, trying to make a top-down shooter and I got some problems setting the virtual joystick(s) to control the ship (character). It works well for a dekstop version (with Input.GetAxis ("Horizontal"), even on iPhone with accelerometer, but can't make it work with joystick. I just need a joystick (left side) to control the ship movement (2D) and a fire button on right. Any suggestions on how to implement these? Tried some iPhone control prefabs that came with Unity (as dual joysticks, etc) but can't make it to work. Are the any other steps involved beside adding the prefab to the scene or assigning the script to the main character (player)? Thanks