May 27 (Reuters) - Acorns Grow Inc said on Thursday it was going public through a merger with blank-check company Pioneer Merger Corp in a deal valuing the savings and investing app at about $2.2 billion. Acorns Grow will receive cash proceeds of over $450 million from the deal, which includes a private placement at $10 per share from investors including Declaration Partners, Greycroft, TPG’s global impact investing platform and BlackRock Inc . Launched in late 2014, California-based Acorns helps consumers invest in stocks and bonds and operates on a subscription-based model that has four million subscribers in the United States. Its merger with special-purpose acquisition company (SPAC) Pioneer Merger, which raised about $403 million in an initial public offering earlier this year, comes after a lull in blank-check dealmaking activity due to increased regulatory scrutiny and saturated investor appetite. SPACs are shell companies that raise funds via a listing to acquire a private company with the purpose of taking it public, allowing such targets to sidestep a traditional IPO. Reporting by Eva Mathews in Bengaluru; Editing by Aditya Soni Our Standards: The Thomson Reuters Trust Principles.