There are fears traffickers intend to sell those on board to fishing trawlers or factories as slave labor in Malaysia and Indonesia.
Bangladesh officials are travelling to southern Thailand to interview 134 suspected victims who say they were on the boat with the 176 others.
All but one of the men and boys say they were kidnapped in Bangladesh and ended up being forced into the hold of a fishing vessel and shipped from the port of Cox's Bazaar to a remote island camp off the coast of southern Thailand.
Many thought they were being recruited for odd jobs in Bangladesh when they were grabbed by unidentified men.
They include a teacher who discovered one of his pupils on the boat.
Three Thai men have been charged with human trafficking after the discovery of the group of 134 in Takua Pa district of Thailand's Phang Nga province.
Police are searching for several others.
More than half of the group had been forced to swim ashore from a remote island after Thai authorities learnt the people smugglers had landed a large group of people there.
The group of 176 are believed to have been taken off the island by the people smugglers before authorities arrived.
Victims have told journalists from Phuketwan, an online news site based in Phuket, they were beaten, abused and given little food by the traffickers.
Sixteen of the victims are Rohingya, a mostly stateless Muslim minority from western Myanmar.
Thailand was downgraded in June to the lowest category, Tier 3, in the US State Department's 2014 Trafficking in Persons' Report for not fully complying with the minimum standards for eliminating trafficking.
The arrival of the boat in Thailand shows that trafficking routes through the country remain open in the southern part of the country where thousands of Rohingya were held and sometimes tortured by traffickers at jungle camps last year, human rights groups say.
Tens of thousands of Rohingya have fled Myanmar since 2012 when violent clashes with ethnic Rakhine Buddhists killed hundreds and made 140,000 homeless.
But most of those on board the latest boat insist they were not willing passengers seeking a new life in Malaysia or another country but victims of kidnappers.
''We have not seen this type of incident before,'' a Bangladesh official told Phuketwan. ''Kidnapping doesn't usually happen in Bangladesh,'' he said.
October is the start of a so-called ''sailing season'' when thousands of Rohingya are expected to risk their lives by boarding boats to flee Myanmar, many of them trying to reach Malaysia where there is a large Rohingya community.