Germany's justice minister has drafted a law that seeks to impose the fines as part of efforts to police toxic chat.
Heiko Maas said the voluntary efforts of social networks to tackle the problem had not gone far enough.
The proposal requires sites to run 24-hour helplines and to delete flagged content within seven days.
'Utterly impossible'
Social media firms such as Twitter and Facebook were getting better at handling illegal content, said Mr Maas, but both had a long way to go.
