For years, we've heard that millennials were afraid of the stock market because of the Great Recession. The market rally since the election may have changed some minds. Nearly one-third of investors age 18 to 34 recently said they plan to move more of their retirement savings into stocks, according to a new survey from MassMutual. While most investors — 60 percent — plan to stay the course with their 401(k)s and other workplace retirement plans, millennials are the most open to changing their portfolios because of the rally, based on a poll of 450 Americans the first week of April. (See table below.)

"I have a large number of millennial clients and I have noticed a definite uptick in the desire to own stocks," said Jonathan Swanburg, a certified financial planner with the Tri-Star Group in Houston, Texas. Last week, Swanburg had two young clients who use the robo-advisor Betterment manually shift their asset allocation from 90 percent to 100 percent stocks. "Clients shifting their own allocations, without first talking to the advisor, is a very rare thing. So two people doing the same shift in the same week is interesting," Swanburg said. " I don't have a problem with it if the clients are educated about long-term investing and matching their investments to their goals."

Investors in their 20s and 30s should be more open to investing their retirement accounts in stocks. Greg Hammond a certified financial planner and CEO of Hammond Iles Wealth Advisors

Many financial advisors like Swanburg see more enthusiasm for stocks among millennials as an encouraging sign. "Investors in their 20s and 30s should be more open to investing their retirement accounts in stocks," said Greg Hammond, a CFP and CEO of Hammond Iles Wealth Advisors in Wethersfield, Connecticut. "Millennials have a long time horizon to retirement and should be focused on long-term growth."

Have a plan and stick to it

MassMutual found that 20 percent of millennials were uncertain about how to invest their retirement savings. For young investors, building a plan can be pretty easy, especially if your workplace retirement plan offers a target-date fund. These set-it-and-forget-it funds automatically invest in a diversified mix of stocks and bonds that become less risky as you approach retirement. Often target-date funds are the default option in your 401(k). If you don't like an off-the-rack portfolio, you can develop your own strategy, use resources provided by your employer if you have them or seek help from a financial advisor, preferably one who is a fiduciary. Begin now if you haven't already and keep investing.