BuzzFeed and Comcast Corp.’s CMCSA -1.80% NBCUniversal revealed new plans to intertwine their ad sales and production, as part of NBCU’s additional $200 million strategic investment in the millennial-focus digital media darling.

The two companies say they will now be able to co-sell ad packages that could include space on each other’s properties. Additionally, BuzzFeed will work with NBCU’s content studio on native ad production and social distribution.

In announcing the new arrangement, the companies officially confirmed the $200 million investment that The Wall Street Journal reported a month ago. That cash infusion doubled NBCU’s investment in BuzzFeed and brings the digital media company’s funding to $496 million to date, according to CrunchBase.

“The investment allows us to remain a fully independent company but have access to and resources from the strongest and best media company there is,” BuzzFeed Chief Executive and Founder Jonah Peretti said in a statement.

BuzzFeed is on target to bring in a little more than $250 million in revenue this year, according to people familiar with the matter. That is up from around $170 million in 2015, which was about 20% below its initial expectations for that year, three people familiar with the matter said.

One of the people said the company is intent on targeting an initial public offering by 2018.

A spokeswoman for BuzzFeed declined to comment.

The most recent investment gave BuzzFeed a post-money valuation of about $1.7 billion, people familiar with the matter said. NBCU’s 2015 investment valued the company at $1.5 billion, meaning that, excluding the new cash, the company’s valuation is essentially unchanged.

Typically, fast-growing startups look to raise their valuations significantly when they receive follow-on rounds of funding. When they don’t, it can signal stress in their businesses or a change of expectations by the investor.

BuzzFeed’s results had been affected by a variety of factors including slower-than-anticipated growth in content-licensing revenue and the difficulties monetizing some platforms where it has a huge audience, such as Facebook, a person familiar with the matter said.

As part of the new investment round, NBCU secured several provisions that protect its position, two people familiar with the matter said. They include the right to additional shares if BuzzFeed’s IPO price comes in lower than NBCU’s investment valuation, as well as being first in line to be paid back if the company is sold.

Write to Lukas I. Alpert at lukas.alpert@wsj.com