The incident followed the Warriors' 24-16 NRL victory over the Titans in Robina on Saturday night.
Tomkins was issued with an on-the-spot $A100 fine by local police and the club has also disciplined him with a $NZ2000 fine.
The Warriors launched an investigation after being made aware of the incident late yesterday.
"We've met with Sam and he admits he made an error in judgement," said Warriors general manager football Dean Bell.
"He knows this kind of behaviour is unacceptable."
Tomkins said he was embarrassed about the incident.
"I'm disappointed in myself. I thought I was in a secluded spot but realise I still made a poor decision," he said.
Bell said the matter had been dealt with and no further action would be taken.
