Newcastle are in the midst of a six-game losing streak and hover just seven points above the drop zone following Sunday's 3-1 home loss to Tottenham.
Off the pitch, fans protested Mike Ashley's ownership of Newcastle outside St James' Park prior to kick-off over the weekend, which resulted in the club's lowest attendance of the season.
"I'm really worried, but I think a boycott's not going to be the answer. I don't think it helps anybody," Shepherd told Sky Sports News HQ.
"We need to get behind John Carver and the team. Doing a boycott isn't going to help that team.
"They're lacking confidence and they need every supporter behind them."
"He'll [Ashley] not want his assets to depreciate, so I'm confident he's going to come out in the summer and spend some money and get some players in," Shepherd added.
"Mike Ashley's a very clever guy. There's no doubt about it - he's a great businessman, so he knows what he's doing."
