The Wall Street Journal: Facebook struggles to figure out how many users it actually has

Facebook Inc. is struggling to detect and deal with users’ creating multiple accounts on its flagship platform, according to internal documents that raise new questions about how the social-media giant measures its audience.

An internal Facebook FB presentation this spring called the phenomenon of single users with multiple accounts “very prevalent” among new accounts. The finding came after an examination of roughly 5,000 recent sign-ups on the service indicated that at least 32% and as many as 56% were opened by existing…