The federal Environment Department said on Tuesdaythe attack occurred March 12, when the victim and three friends went to the La Encrucijada reserve to fish.
The 18-year-old man was carried off by the reptile, but his companions escaped.
The department said it would erect crocodile warning signs.
The department said experts and fishermen began working Tuesday to locate crocodiles of that length in a swampy area on the Pacific coast of Chiapas state.
Experts will try to capture and empty the stomachs of the crocodiles without killing them to see if any contain human remains.
If they find the animal, it will be relocated to an animal reserve, park or zoo.
The Natural Protected Areas Commission said “the majority of these incidents are caused by people who unknowingly enter areas where fishing is not permitted.”
Still, the commission expressed its condolences for the man involved in the attack, saying it is “committed to the absolute respect for human life.”