London — SupersonicAds, a social in-game advertising platform developer, raised $4.2 million from Greylock Partners to help compete with other international markets.

The new funding will help the start-up expand its London sales team while integrating its services deeper into other games VentureBeat reported. It also is working on developing a mobile service.

SupersonicAds helps monetize international players with pay-per-engagement advertising, which can be applied to incentive programs like unlocking new features or earning in-game currency.

The company’s clients include Kellogg’s, Dell, Groupon, Skype, Disney and Dell.

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