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Investors looking to buy stocks with no commission have many options: Upstarts like Robinhood and SoFi and, in more recent months, traditional brokerages including Charles Schwab. But despite this crowded market, a startup backed by actor Will Smith and NFL star JJ Watt sees an opportunity to snap up customers.

The new entrant is called Public, which premiered in September, and on Monday, touted an additional $15 million in investment led by the venture capital firms Accel and Greycroft. The startup hopes to distinguish itself by offering retail investors a Pinterest-like social media environment where they let others know which stocks they buy.

A core element of the Public app is a stream that lists who bought or sold shares in various companies along with comments from those users and others on the service. The app also offers streams —along with communities of users—based on user interests such as female-led companies or those committed to fighting disease.

According to Ian Sigalow, a partner at Greycroft, the social element gives Public an edge versus its many competitors, in part because viral sharing helps the company acquire new clients for free. He compared this model to companies like Robinhood, which Sigalow claims rely on paying platforms like Facebook to win customers—often at a cost of more than $100 per user.

Sigalow believes Public can follow in the footsteps of one of Greycroft’s earlier investments, Venmo, the popular peer-to-peer payment service.

“What made Venmo so special was that it was a social network masking itself as a payment service,” he said, adding that Public’s users create content that lead people to open the app more frequently.

For now, Public’s celebrity investors Smith and Watt have yet to publish their stock purchases on the platform, though the startup suggests they may do so in the future. Sigalow also notes that NBA legend Shaquille O’Neil recently opened an account.

The idea of building a social network around stocks is not new. A company called eToro, for instance, has won millions of customers in Europe by allowing users to follow and mimic the investment choices of others on the platform. eToro also promotes leading traders.

Such features have been slow to catch on in the U.S., however, in part due to uncertainty over whether the Securities and Exchange Commission may treat social media posts as investing advice.

Sigalow says he is confident that Public will not encounter regulatory issues, and that the company has invested heavily in compliance. He also points out that users must actually buy or sell a stock in order for it to show up as a new post in the social media feed—something that limits the reach of spammers or would-be market manipulators.

Public, which has 35 employees and offices in New York and Copenhagen, is also one of a growing number of companies, including SoFi, that allow customers to buy fractions of a share. Sigalow says this is important because it allows investors of modest means to buy companies like Google or Amazon, whose stocks trades above $1,000. Public also offers investors a high interest rate, currently 2.5%, on idle cash in their accounts.

The startup has not disclosed its financials, but says it earns revenue by loaning out shares to short sellers, as well as from payments obtained by routing orders to certain exchanges. Public also makes money from interest on cash balances.

The company’s co-CEOs Leif Abraham and Jannick Malling would not publicly disclose how many users Public, which has raised a total of $24 million to date, currently has. Instead, they state that the app’s user base has seen 20% week-over-week growth.

Public believes one tool that will cause its user numbers to swell is a gifting feature, which lets users send stock to their friends, including in amounts as small as $5. Such gifts, says Sigalow, will fuel an “insane virality” that will help Public breakthrough in a market where consumers have a surfeit of platforms to buy stocks.

Public, a would-be Pinterest of stock-buying apps, raises more cash

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