Fidelity's Contrafund led the way, holding 1.1 million shares at the end of November, according to the latest available fund disclosures. That stake was worth $73 million on Monday, a small bet for a fund with net assets of $109 billion.
In contrast, Contrafund's stake in Facebook was worth $1.6 billion at the end of November. Some analysts say Twitter may lose out to Facebook and Google in the battle for online ad revenue.
In all, nearly 30 Fidelity funds bought Twitter shares, according to data from Fidelity and Lipper, a Thomson Reuters company. Fidelity declined to comment.
Twitter stock is up 155% over its November 7 initial public offering price of $26 per share. But investors are debating whether it will become just a social media niche or achieve the giant status of Facebook.
The stock fell 4% on Monday to a close of $66.29 after analysts at Morgan Stanley downgraded Twitter to "under weight" from "equal weight" and questioned how much online ad revenue it would collect in relation to Facebook and Google.
Nevertheless, Twitter's stock market value is a frothy $37 billion, despite being a money-losing operation. And US mutual funds are sitting on some handsome gains since the IPO.