AFP, SAN FRANCISCO: The parent of the fast-growing social network Snapchat filed public documents for a share offering Thursday, seeking to raise up to $3 billion in a keenly anticipated Wall Street debut. California-based Snap Inc., which had earlier filed confidential documents for an initial public offering, was expected to be one of the biggest tech company IPOs in recent years with a valuation likely to top $20 billion. In documents filed with the Securities and Exchange Commission, Snap said it took in $404 million in revenue last year but lost $515 million. Snapchat, known for its disappearing messages, has become hugely popular with young smartphone users. But the company has recently been expanding its offerings to allow publishers to deliver content through the platform.