Softbank and Google are set to be among the big paper winners in an initial public offering of the social gaming business reportedly valuing the company at $15bn to $20bn.

The online game company, whose backers include US-based search engine Google and Japan-based telecoms and media conglomerate Softbank, plans to raise $1bn and reportedly up to $2bn in its flotation on an undisclosed US stock exchange.

In July last year, news provider New York Times reported recent investments by Google and Softbank had totalled a combined $300m. Softbank later confirmed an investment totaling $150m, while Zynga verified Google’s involvement for an undisclosed amount.The public filing for Zynga’s listing