Holly Alexander said her two-year-old doberman rottweiler cross Ester escaped from her cage on Monday night while aboard the Spirit of Tasmania.

It remains unclear what has happened to the lost pooch.

Ms Alexander said she checked the cage's lock twice before she was awoken by a security guard at midnight and told Ester had disappeared.

"(They) had been trying to get her but had no luck," she wrote in a Facebook post.

"They would only let me look for an hour and I waited in the bar as they kept looking.

"They couldn't find her, they didn't raise any alarms when they were trying to get people to disembark or check their cars as they seem to think that she might of (sic) jumped in the utes or trailers."

Ms Alexander said she stayed at the dock until midday on Tuesday refusing to leave and security cameras didn't shed any light on Ester's whereabouts as they were not facing the kennels.

"She is my best friend and I just want her back," she said.

"Not knowing if she's dead or alive is killing me."

She is moving to Tweed Heads in Queensland and is hopeful Ester found her way into a vehicle during the crossing.

The Spirit of Tasmania told AAP in a statement it was closely working with Ms Alexander to find Ester and was asking passengers who were on board the ferry to check their vehicles.

"Despite a thorough search of the vessel, Ester has not been found suggesting that she may have left the vessel inside another passenger's vehicle or trailer," the company said in a social media post on Wednesday.

"If you have seen Ester please send us a direct message with your contact details. Please help return Ester to her owner."

Australian Associated Press