Mr Fenwick, 33, also known as "Feno", was last seen after midnight on January 31 when he walked with his girlfriend, Samantha Melville, from Fern Bay to Corroba Oval, on the corner of Fullerton and Meredith streets at Stockton, police said.

Ms Melville left him at the oval to walk to a house, but he was gone when she returned.

He has not been seen or heard from since.

"I was supposed to meet back up with him and I rang him and, yeah, his phone was off," Ms Melville told Nine News.

"He was a nice guy, you know, he would pretty much go out of his way to do anything for anyone."

Mr Fenwick's mobile phone and clothes were discovered in sand dunes near the southern end of Stockton beach and sent for forensic examination.

But detectives believe the clothes may have been planted by whoever murdered Mr Fenwick in a bid to make it look like he went for a swim and drowned.

The discovery of those items led PolAir, Police Rescue and the Marine Area Command to launch several land and sea searches in the days following his disappearance.

Those searches uncovered little and were eventually pulled back as the police investigation shifted focus onto the people who knew him.

Newcastle detectives have established Strike Force Kummari to investigate Mr Fenwick's disappearance and suspected homicide.

"Police hold grave concerns that Steven could be the victim of foul play and the case is now being investigated as a suspected homicide," police said in a statement.

Mr Fenwick was last seen wearing a black shirt, black board shorts, a red cap and grey/blue thongs.

Detectives are renewing their appeal for anyone who may have information about Mr Fenwick's disappearance to contact Crime Stoppers on 1800 333 000 or call the Newcastle City police station directly on (02) 4929 0999.