A woman received a huge shock when she found a naked stranger perfoming an indecent act inside her home in Melbourne's west.

Police said the woman was at her Hogans Road, Hoppers Crossing home on Saturday, April 5, with friends and family when she walked to the back of the house about 10.45pm.

As she walked past a bedroom, she saw a naked man, believed to be a teenager, lying on a bed, performing an indecent act.

She called to her husband for help, and the man jumped off the bed and ran out of the house through the laundry door.

He climbed over the back fence, still naked, and ran off towards Tarneit Road, Hoppers Crossing, police said.

Police have released a digital image of a man, described as being in his late teens, about 180 centimetres tall, with straight, light brown hair, and a small tattoo on his left shoulder.

Anyone with information is asked to contact Crime Stoppers on 1800 333 000.