Translation:Facebook and Twitter are two popular social media.
In English I think we might be more likely to say "two popular social media sites" or "popular media services"
In North America we would most likely say "two popular social networks or social media networks".
It's not singular in this sentence but neuter plural.
Are names of websites like this never transliterated into Greek? Even if someone were writing this sentence by hand?
They can be transliterated. It is just the personal preference of the writer to write them in Latin or Greek script.
I'm glad that proper English was put in as acceptable answers but i was just presented an option where proper English was not possible as an answer. Perhaps the primary correct solution needs to be updated.