Police are appealing for witnesses after a naked man approached a teenage girl near Port Stephens last month.

About 2.30pm, Thursday 21 January 2016, two 15-year-old girls were at Boat Harbour beach, 15km south of Port Stephens, when one of the teens went for a swim.

A short time later she got out of the water onto the rocks, when a naked man approached her.

He sat down beside her, before the other girl approached them and the man walked away.

As the girls left the area they saw the man committing a lewd act.

The pair walked home and informed one of their fathers, who contacted police.

Officers from Port Stephens Local Area Command attended and commenced an investigation.

Police patrolled the area but could not locate the man.

As inquiries into the incident continue, police have released an image of a man who may be able to assist them.

He is depicted in the image as being of Caucasian appearance, aged between 50 and 60, with grey hair, solid build and wearing a black baseball cap.

Investigators are also appealing for anyone who witnessed the incident, or anyone who may have information that will assist with their inquiries, to come forward.