The trick, it would seem is to get them to invest. According to Transamerica Center for Retirement Studies, millennials need the guidance of a broker—52 percent admitted to guessing what they should be saving. Only one in 10 used a retirement calculator or worksheet. The Transamerica data shows they're interested in guidance—61 percent want some level of advice, though just 32 percent actually have used an advisor.

Getting Them Talking

Michele Gasparre, president of Meridian Benefits Consulting in Westchester, NY, said millennials are much more amenable to hearing their investment options than brokers first thought. She works with a number of plans with participation ranging from 60 employees to 600 employees. "We get 80 percent participation in that age sector."

Gasparre said millennials are quite serious about retirement, partly due to watching their parents go through the economic recession since 2008. Also, Gasparre said many younger investors know that Social Security benefits won't be an option for them. Plus, many are looking at a longer retirement.  "They don't want to wait until they're in their sixties to retire—they want to retire earlier," she adds.

Clarke Hedrick said if anyone had asked him prior to 2008 if there was a problem selling to the younger crowd, he'd have said "yes". Now, he thinks a combination of the economic downturn and technology taking over the financial sector have contributed to both an awareness and ready access to investment tools and real-time research and information. Hedrick, president of Pivotal Financial Services in Commack, NY, said most major fund companies have the technology that makes proactive investing easy.

Hedrick still thinks one of the best ways to reach the millennial generation is through education. "We want to be engaging with these people, whether it's on their 401(k) plan or their benefit plan, so they fully understand what opportunities they have, how it works, why it works."

Breaking it down for them helps, said Gasparre. She demonstrates to younger participants a 24-year-old making $40,000 annually, investing 15 percent with a six-percent rate of return and an annual four-percent salary increase. By age 68, that investor will have amassed $2.3 million. The 30-year-old investor just starting a retirement fund, she said, will net just $1.4 million. These types of illustrations show just how much money millennials can leave on the table if they don't invest as soon as possible, she said. "If you wait 15 years, it's going to cost you a million and a half dollars."

In a world of instant gratification, convincing young investors to sock money away for 30 or 40 years can be challenging. Giving them real-world examples of the importance of retirement investing is a great tool.

James Sampson, managing principal of Cornerstone Retirement Advisors in Warwick, RI, said the usual arguments—"I can't afford it"—is real, but brokers can help them overcome that feeling of being stretched too far. "We get them to start saving as high as they can, whether that's 2 or 3 percent or 5 or 6 percent. Just get started."

From there, he prescribes the one-percent difference – increase the amount by one percent each year. "If you do it every year religiously, you'll wake up one day saving 15 percent of your income," he said.

Sampson tells of an experience at one of his benefit meetings. A client relationship manager had accompanied him. He asked her to tell her story. She was a mother of five when she suddenly got divorced. Forced back into the workforce in her mid-forties, she worked at a liquor store as a cashier making $17,000 annually. Reluctantly, she was convinced by a broker to invest two percent of her income in a 401(k). She increased that amount by one percent every year and now invests 18 percent annually.

Her experience made an impact. Sampson says the participation in that company's 401(k) went from 69 percent to 90 percent in one year, and investments increased from 3.47 percent to over 6 percent.

Keeping Them Talking

Beyond face-to-face, once-per-year meetings, brokers are using the monthly newsletter, monthly meetings, webinars, and Twitter follows to keep millennials participating in the retirement conversation. Hedrick suggests being present on social media, where young investors are, and keeping the dialogue helpful and interesting.

Also, Gasparre said brokers should be teaming with the fund providers to improve participation for millennials. "Once a year is not enough. Quarterly at the very least and not necessarily face-to-face. It's between the broker and the financial advisor to really engage the population regardless of their age."

That's a key step, said Sampson, who points out that millennials use technology regularly, but in moderation. "While technology is obviously crucial, it's important not to lose the personal touch."