When looking for a job in Sofia, it would be a good idea to start your search by checking the website of the National Employment Agency.
Some of the most popular job portals in Bulgaria include (and are not limited to):
LinkedIn is also becoming an increasingly popular platform for finding jobs in both Sofia and Bulgaria.
There is a strong expat community in Sofia and Bulgaria, so there is a number of expat-related blogs and websites, where you can find interesting job opportunities.
For EU-wide vacancies, please check the European Job Mobility Portal (EURES).
Don’t forget to check the ‘HR Contacts’ section of Sofia’s profile @SCALE: https://startupcityalliance.eu/sofia/setting-up-your-company/legal