Since 2009, Sithen has mobilized thousands of young Cambodian film enthusiasts, laying the foundations for their careers through intensive workshops, mentorship, and festival showcases, including the Chaktomuk Short Film Festival (CSFF) and the Southeast Asia Video Festival for Children. He gained commercial production experience at PuPrum (2016-2017) and later worked as a marketing consultant for DancingRains Production (2019-2021). In 2018, he completed a film producing course at the Busan Asian Film School in South Korea. As the founder of Sunflower Film Alliance (2017) and Sunflower Film Organization (SFO) (2019), he has been dedicated to training Cambodian and Indigenous youth in filmmaking, particularly through the Let's Document Cambodia program. Since 2019, he has expanded SFO's and CSFF's international collaborations, forging partnerships across Asia. To sustain SFO's operations, he launched Sunflower Media in 2022, a social enterprise providing video production and training for non-profits and social enterprises. His work also extends to film programming, youth development, and peacebuilding. Currently, he advises Norton University senior students on their Creative Multimedia short film theses while developing a film studies curriculum for the university. As a film educator, he emphasizes hands-on learning over theoretical approaches. Sithen is a Salzburg Global Fellow.