Trump's tweets are driving millennials to make a rookie investing mistake

When @realDonaldTrump tweets, investors pay attention.

The President-elect's early-morning jabs at large companies have repeatedly moved the market. And no other age group reacts to tweets like millennials, according to E-Trade.

In a survey of 904 people, the brokerage found that 60% of those aged 25 to 34 had traded off a Trump tweet. They all managed at least $10,000 in an online account and traded between January 1-10, according to E-Trade.

The share of traders that bought or sold because of a Trump tweet fell as years advanced: it was 36% of those aged 35 to 54, while just 20% of people over 55 reacted to a tweet.

That's a sign of shortsightedness among younger traders and may not serve their portfolios well if it's not balanced with longer-term strategies, said Mike Loewengart, E-Trade's vice president of investment strategy.

"Older investors have lived through many more market environments and they are cognizant of the fact that what the president-elect says is much less meaningful in the longer term," he told Business Insider on Thursday.

"The concept of long-term compounding of growth becomes crystallized for someone who's experienced," Loewengart said. "It doesn't necessarily become clear to us that a long-term view is coming through" in millennials' thinking when they hurry to trade after Trump tweets, he said.

Short lived moves

Some of the stock moves right after Trump's tweets proved to be short-lived. For example, Boeing shares slipped in early December, after Trump said the company should cancel its new Air Force One order because the costs were "out of control." But the stock gained nearly 4% in the three weeks that followed.

This doesn't mean Trump's tweets should be irrelevant to markets. In fact, investors don't really have a choice but to monitor his account, according to Larry Adam, the chief investment officer (CIO) for the Americas at Deutsche Bank Wealth Management.

"I guess it's the maturation of a strategist or CIO," he said at a press event last week. Twitter is set to become a fixture of trading floors just like TVs were necessarily set up to show market-moving events, he added.