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Peter Thiel, whose Valar Ventures fund has backed Trading Ticket.
Trading Ticket operates TradeIt, a service that lets readers buy and sell stock from within news reports after the sign up with their brokerage.
Say you're reading a report on Apple that you like - next to the company's name you'll find a button that lets you trade that stock and buy more.
Over 80% of orders placed since launch earlier this year have been on mobile, according to the company.
Trading Ticket's co-founder and CEO Nathan Richardson says in a statement that the company plans to use the seed funding from Citi and Valar to "expand our footprint and build new inroads across the industry."
Trading Ticket first showed up on Citibank's radar earlier this year, when TradeIt won "Most Innovative Trading Solution" at Citibank's Global Mobile Challenge.
As part of the deal, Valar Ventures' Andrew McCormack is joining the board. He said in a statement: "Trading Ticket's technology position, seasoned leadership team, and strong reception with both established and new financial services players is impressive.
"We believe the global opportunity for integrated, mobile trading is very promising and Trade It is well positioned to capitalize on its most valuable areas."