The Committee to Protect Journalists (CPJ) fear for the lives of the seven other identified journalists believed to be captives of the ISIS.
According to CPJ, Syria had always been the most perilous country in the world for journalists for more than two years now.
James Foley is just one among the estimated 69 journalists who were killed in Syria, or over the border in Lebanon and Turkey.
"Local and foreign journalists already knew that Syria was the world's most dangerous place to be a reporter before the beheading of James Foley brought that knowledge to the general public. The members of the Islamic State who murdered him use violence and intimidation to silence all independent reporting in the areas they control," CPJ Deputy Director Robert Mahoney said.
Approximately 20 journalists, with the majority of Syrians, are still missing in the country.
Seven of these missing journalists are believed to be held captives by the ISIS, CPJ reports.
One was identified as Aboud Haddad, a freelance photographer who worked for the Syrian opposition TV station Orient News. He was abducted on June 26 2013 in the city of Atma in Idlib province.
Mohanad al-Sayed Ali, the station's head of news reporters believed that Obadiah Batal, correspondent for Orient News, broadcast engineer Hussam Nidham al-Deen, and assistant engineer Aboud al-Atiq were also being held captive by the ISIS.
Muayad Saloum, another Orient correspondent, was abducted on November 2013. Conflicting reports claimed he had already been executed while Ali said this information was not confirmed.
Rami al-Razzouk, a journalist for the local news outlet Radio ANA, was abducted on October 1, 2013, after gunmen raided Radio ANA's office. Radio ANA's founder, Rami Jarrah, confirmed to CPJ that al-Razzouk is still being held captive by the ISIS.
Shahba Press correspondent Yassir al-Sattouf, also known as Abu Ahmed al-Dir Hafiri, was kidnapped on November 20, 2013. His abduction took place after he condemned ISIS' invasion of important government buildings.
Meanwhile, Australia's minister for communications, Malcolm Turnbull, has called for media chiefs to reflect on the death of Foley.
In a keynote speech given at the Newspaper Works industry conference in Sydney, Turnbull highlighted the very high price that many journalists pay to bring people the truth.
"Journalists and journalism are in the front line of the battle for democracy. I condemn the murderers of James Foley, extend our condolences to his family and express the support of our government to all journalists, including our own Peter Greste wrongfully imprisoned in Egypt, who are paying a high and all too often cruel price for freedom's sake," Turnbull said.
20 Deadliest Countries To Be A Journalist With The Corresponding Number Of Journalist Deaths (Data From CPJ)
1. Iraq: 165
2. Philippines: 76
3. Syria: 67
4. Algeria: 60
5. Russia: 56
6. Pakistan: 54
7. Somalia: 53
8. Colombia: 45
9. India: 32
10. Mexico: 30
11. Brazil: 29
12. Afghanistan: 26
13. Turkey: 21
14. Sri Lanka: 19
15. Bosnia: 19
16. Tajikistan: 17
17. Rwanda: 17
19. Sierra Leone: 16
20. Bangladesh: 14