Arisman's escape came as Thailand's deputy prime minister said the government had ordered security forces to move against what he said were "terrorists" inside the hotel.
Suthep Thaugsuban said the operation was aimed at capturing the leaders responsible for last Saturday's deadly clashes in Bangkok which left 24 dead and hundreds injured.
"As I am speaking, special forces are surrounding the SC Park Hotel where we believe the terrorists and their leaders are staying," Suthep said on national TV.
Government officials later admitted that the raid on the hotel had been unsuccessful.
In his address Suthep also urged "innocent" protesters to leave the Ratchaprasong area of Bangkok, a vital commercial area of the city, which has been the focus of recent red shirt rallies.
"I would like to ask innocent protesters to leave the demonstration area, in order to avoid being used as human shields," he said.
"The government from now on would like to carry out decisive legal measures against the red shirt leaders.''
The government has previously blamed "terrorists" for Saturday's violence.
Abhisit Vejjajiva, the Thai prime minister, said on Friday that he had made Anupong Paochinda, the army chief, the head of the National Security Agency, replacing Suthep.
The move was made to streamline operations and restore order, according to Abhisit.
Most of the red shirt protesters are supporters of Thaksin Shinawatra, the former Thai prime minister who was ousted in a 2006 coup.
The SC Park hotel is owned by Thaksin's family.
Al Jazeera's Tony Birtley, reporting from outside the hotel, said the situation was very tense and a small incident had the potential to erupt into violence.
He said there was a lot of rumour and speculation among protesters that the raid on the hotel was the beginning of a government-ordered crackdown.
Friday's move came after red shirt leaders said earlier this week that they were regrouping for a final confrontation with the government, after more than a month of non-stop protests.
Red shirts' demand
The red shirts are demanding that Abhisit stand down and call fresh elections, saying his appointment by a parliamentary vote in late 2008 was illegitimate.
However on Friday Korn Chatikavanij, the Thai finance minister, said Abhisit had no plans to quit.
Resigning the leadership at this time would "be very negative for the country", he told the Reuters news agency.
Larry Jagan, a Southeast Asia analyst, told Al Jazeera that with the Songkran Buddhist new year holiday now over, both sides were likely to step up their confrontation.
Speaking from Bangkok he said most people saw the red shirts were in the driving seat and there was increasingly little doubt that Abhisit would have no option but to call a fresh election.
"It's a question of when rather than if," he said.
The escalating crisis has badly dented investor confidence in the Thai economy and caused thousands of visitors to cancel holidays in Thailand, threatening the country's vital tourist industry.