AdRoll raises $70 million as its expands ‘retargeting’ into mobile

FORTUNE — Ad tech isn’t sexy, but it still can generate a lot of venture capital dollars. Case in point is AdRoll, which this morning is announcing $70 million in new funding led by existing shareholder Foundation Capital.

AdRoll is a San Francisco-based company founded in 2007 to focus on digital ad “retargeting,” a process whereby merchants and marketers can find you on the web even after you’ve left their site. For example, imagine you’re on your laptop shopping for a shirt at but then something comes up and you turn off your browser rather than completing your order. When you go back online to check the weather forecast, there’s a decent chance that you’ll see an advertisement for Target (TGT).

One big problem for ad re-targeting has been the rise of multiple devices, since you might actually check that weather forecast on your phone rather than on your laptop. AdRoll co-founder and president Adam Berke acknowledges the challenge, but says it’s one that the company is beginning to solve.

“For example, we have integration with Twitter (TWTR) called ‘tailored audiences,’ which lets us identify a user who gives an intent signal on his desktop,” Berke explains. “Then Twitter gives us a handshake on the backend so we can identify that user when he shows up on his mobile device, so we can serve an ad to him there. We have something similar with Facebook (FB).”

AdRoll plans to use some of the proceeds from the new round to bulk up this cross-device infrastructure, as well as for geographic expansion. The company opened its first international office last year in Dublin with 40 employees, and plans to have 100 there by year-end. It also just opened an office in Sydney, Australia. Overall, AdRoll has around 400 current employees and plans to add around another 250 by year-end. “We’re basically hiring one new person per day,” Berke says.

The company reports a $150 million revenue run-rate, compared to a $50 million pace in early 2013 (and $100 million last October). It used to also talk about profitability, but now seems content to accept losses in exchange for growth. Those are the sorts of numbers that likely could have helped the company price an IPO rather than take big new venture funding, but Berke suggests that the company wants to be stronger (both in terms of product and balance sheet) before possibly heading out into the public markets.

Foundation’s agreement to lead the round is unusual in that it is an existing investor in AdRoll, but the move is not unprecedented.

“We believe strongly that we should back our winners with as much capital as we have available if they are experiencing explosive growth in to huge markets with strong management teams that have a proven track record of success,” explains Foundation partner and AdRoll board member Charles Moldow. “The objective is to still make a venture return (10x) even at the late stage given all that we know and believe will transpire into the future. Our most recent demonstration of pursuing this strategy was when we led the $1.55 billion valuation Series E round at Lending Club after previously leading the Series C.”

New investors in the deal include Institutional Venture Partners, Northgate Capital, Performance Equity and Glenmede, while other return backers include Merus Capital, Accel Partners and Peter Thiel. IVP principal Eric Liaw will join the AdRoll board as an observer.

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