Currently there are 11 native Telephoto Prime lenses for Olympus E-M5 and 7 of these lenses are autofocus (AF) type.
E-M5 also has a sensor based image stabilization system which means that all of these lenses will be stabilized when used on E-M5.
Since Olympus E-M5 has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 4 Telephoto Prime lenses with Weather Sealings.