Authorities have checked footage from 15 CCTV cameras in the area and saw what they consider to be suspects who may have placed the bomb. Their identities were still unknown.
There was wide sharing on social media of a report about "a white foreigner" who arrived in a tuk-tuk carrying a rucksack, and then was seen without it. Later the bomb went off.
Police have swept the streets in the Ratchaprasong area looking for possible evidence. The intersection remained closed, causing traffic jams in the area, but was expected to reopen about noon on Tuesday.
The bomb blew debris and shrapnel up to 100 metres from site of the explosion.
The hotline 1599 is open for the public to contribute photos or videos taken around the area before or soon after the bomb explosion, to help authorities reconstruct the crime.
Ball bearings possibly packed with the explosive as shrapnel were found in the explosion area. They were six millimetres in diameter, the same size as those found at the scene of the botched bomb explosion set off by Iranian suspects on Sukhumvit 71, Bangkok, in February 2012.