The stock market continued to gain ground on Monday, reflecting investor optimism about the potential for a favorable outcome in the planned U.S. meeting with North Korean leader Kim Jong Un in Singapore. Most major benchmarks gained modestly on the day, with the Nasdaq Composite rising and the Dow Jones Industrial Average picking up a few points. Some companies had particularly good news that sent their shares substantially higher. Fitbit (NYSE:FIT), Genworth Financial (NYSE:GNW), and Roku (NASDAQ:ROKU) were among the best performers on the day. Here's why they did so well.

Fitbit looks fitter

Shares of Fitbit rose 15% after the maker of wearable devices earned favorable comments from noted short-selling analyst Andrew Left at Citron Research. Citron believes that Fitbit's moves to broaden its usefulness to the healthcare market could be a growth catalyst that might send the stock to as much as $15 per share by the end of 2018, which is more than double their current price even after today's jump. Citron also speculated that a buyer might emerge to acquire Fitbit before the stock had a chance to climb that high, potentially resulting in a more immediate payoff for shareholders. If Fitbit's digital health initiatives are successful, investors might well prefer to hold out for a lot more than $15 per share.

Black Fitbit device.

Image source: Fitbit.

Genworth gets the green light

Genworth Financial stock soared 26% after the financial insurance company got a regulatory go-ahead for its would-be acquirer to move forward with its purchase transaction. Chinese real estate and finance specialist China Oceanwide Holdings Group had bid $2.7 billion in late 2016 to purchase Genworth, but concerns about whether the Committee on Foreign Investment in the U.S. would approve the deal had led to a long delay. Many believed that the acquisition had a poor chance of happening. Yet today, CFIUS gave its OK for China Oceanwide to move forward. That had Genworth investors breathing a sigh of relief after a long wait.

Roku receives a thumbs-up

Finally, shares of Roku jumped nearly 6%. The video programming company received favorable comments from analysts at Keybanc Capital Markets, who said that they see faster growth in customer counts using the company's platform. Between greater support from advertising on Roku's own channel and distributors of other video programming looking to be on the Roku platform, Roku has the opportunity to become an even more attractive alternative to traditional cable television services. Keybanc has rated Roku overweight and set a $44-per-share price target, which is only about 5% higher than where the stock is likely to close today.