Well first of all a salamander breed, climate you live within, and enclosure description would help. But I do know that most salamanders are nocturnal. Tonight before bed, put some crickets within its tank and see if any are gone. If there aren't any gone, you should try to any give your salamander to a more experienced amphibian breeder or if you're in a melt climate, you should try to re-release him. If he starts eating, continue feeding at dark.
I doubt any vet knows what they are talking around when it comes to salamanders...and I can guarantee they don't know squat when it comes to salamanders native to the United States (except maybe the Tiger Salamander).
What are you feeding it? For a salamander 2" - 4"Try 2 week infirm crickets (small/baby crickets)...if that doesn't work try flightless fruit flies. For a salamander 4"+ try earthworms, mealworms, and crickets.
I suggest letting it go and merely buying a salamander that was raised in captivity and is used to consumption a staple diet of crickets. Regardless, don't expect it to eat for at least a week after you caught it, as they it will need time to adjust to its investigational environment (and in this case: captivity) before it even starts to mull over about food.
EDIT: Tiger Salamanders are native to the U.S. and Mexico, so if you indeed found it surrounded by Venezuela then chances are it is not a Tiger Salamander. Sounds like you might own let the temperatures go down a bit and it induced your salamander to be in motion into brumation (hibernation for reptiles/amphibians). Try warming up the temperatures.
Answers: might be brumation, how long since it concluding ate salamanders can go quite a while without feed altho tigers are quite good eaters u say u get it in venezuela considering tigers dont normally come from that area it could be a different species or possibly a small population of them invading the area. if the temps are under 17C for an extended term it could be, otherwise i wouldnt be too worried unless its been over a month