Green’s Dictionary of Slang

(UK/US teen) the ‘fear of missing out’.

2011		IOL News (Western Cape) 19 Apr. 🌐 Common phrases used by British teenagers include ‘peng’ meaning a person who looks good and ‘fomo’, an abbreviation of fear of missing out.
2014		C. Eble UNC-CH Campus Sl. Spring 2014.
2016		C. Eble UNC-CH Campus Sl. Spring 2016.