Their families say they will be going to Mexico amid media reports that two unidentified bodies were found inside a burnt-out van resembling theirs.
A family statement said they hold "deep fears" but police did not comment.
"Dean and Adam were travelling in a van, departing from Topolobampa on Friday 20 November to Guadalajara but did not arrive on their scheduled date," a joint statement said.
"The families hold deep fears for the safety of their sons but stress that they are still waiting for details to be confirmed."
Australia`s Department of Foreign Affairs has confirmed it is providing consular assistance to the families.
Dean Lucas` girlfriend, Josie Cox, posted a message to Facebook saying she was devastated after learning how he was going to propose.
"I definitely don`t doubt that there`s something that`s happened, something that we should be worried about," she told the media.
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