"While the total number of people who have been impacted is small, we take any threat to security seriously and are redoubling our efforts to combat the scam," Facebook engineer Alok Menghrajani said in a blog post.
Cyber-criminals trick people into revealing Facebook account names and passwords at bogus Web pages, and then assume their online identities.
"Once they've logged in, the scammers send Facebook Inbox and Chat messages and may even post status updates to the person's profile asking friends to send money, usually through Western Union," Menghrajani said.
Facebook is working with Western Union, a message and money transfer service, which has posted warnings at its website about the 419 scam.
Facebook said it has improved automated systems to deal with the scam and is collaborating with police and email services to catch those behind the cons.
Menghrajani urged Facebook users to become "fans" of the social-networking service's security page, which offers advice about avoiding scams and reporting suspicious activity in the online community.
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