KEY POINTS
  • Morgan Stanley on Thursday lowers its rating to underweight from equal-weight for Roku shares.
  • The firm's analyst says the stock's valuation at more than 17 times estimated 2018 platform sales is too excessive.
  • Roku shares fell 6 percent Thursday.
People pass by a video sign display with the logo for Roku, a Fox-backed video streaming company, Sept. 28, 2017.

Investors should take profits after Roku shares nearly tripled following its earnings report, according to a top Wall Street firm.

Morgan Stanley on Thursday lowered its rating to underweight from equal-weight for Roku shares, citing the company's high valuation.