It's no secret that Twitter (TWTR) is struggling to grow its user base. Indeed, the social network's number of users declined from 307 million to 305 million between Q3 and Q4 when excluding the company's SMS Fast Followers, or lower-value users who access the service through text messaging primarily on feature phones. Meanwhile, Facebook's (META 0.11%) user growth is thriving. What advice would Facebook give to Twitter about the smaller social network's user growth problem?

This week we found out exactly what Facebook would say -- straight from the mouth of Facebook CEO Mark Zuckerberg.

Mark Zuckerberg at Facebook's "townhall" in Berlin. Image source: Facebook.

Facebook to Twitter: Make it easier to keep up with public figures
"Considering the current state of Twitter, if you were the CEO of Twitter, what would you do right now?" asked an audience member during Mark Zuckerberg's "town hall" question-and-answer session in Berlin, Germany, this week.

Seeming a bit startled by the question and initially stumbling with words and chuckling, Zuckerberg gathered himself and proceeded to give his best answer: 

Let me answer that question by talking about what we've done with Instagram. ... Facebook traditionally has been a service that is mostly focused on, you know, more private communication with friends, small groups of people. And one of the things that I think, traditionally, other networks and other parts of the Internet -- and whether that's Twitter or YouTube or different communities -- have traditionally done more on is on public content. And, you know, recently, with Instagram -- and Facebook as well -- that's an area that we can just focus a lot on.

Facebook Live makes it easier for users to connect with public figures. Image source: Facebook.

You know, people want to keep in touch with, you know, the athletes that they care about, the celebrities and the actors who they care about, political leaders -- you know -- civil leaders in their communities. And giving people tools to be able to share what they care about, and follow those things, I think it has contributed to a large degree in the growth of Instagram. Right? And I think it has historically to the growth of Twitter, too. And I think that there's probably more that they can do there.

But it's certainly an area we're seeing with Instagram. ... Instagram joined us when that community was -- I think it was about 20 million people. And the team that was working on Instagram at the time was 14 people. At the time, everyone was like, "Ah, you bought that for a billion dollars? You're crazy." And, you know, maybe we are a little. But, you know, since then, we've helped build the team up. It's ten times bigger now. And we have 150 people -- of the best people at Facebook -- working on Instagram. The community has grown from 20 million people to more than 400 million people on Instagram now. Instagram is now bigger than Twitter.

And I think a lot of that is because we've executed the roadmap that I'm talking about in terms of giving people the ability to -- giving public figures and folks the ability to produce great, kind of, raw content of what's going on in their lives and giving people the ability to connect with that.

Finally, Zuckerberg summed up his advice as distinctly as possible:

There's a lot more that I think needs to be done to give people the ability to connect with the people and figures that they're interested in. And I think that you're going to see a lot of that on Instagram and on Facebook. And if the Twitter folks do a good job, I think you'll see a lot more of that on Twitter, too.

One of the examples Zuckerberg cited as a way Facebook is making it easier for people to follow public figures is with its Facebook Live, which enables users to broadcast live on Facebook. Illustrating the company's commitment to the feature, the company announced this week that Facebook Live is going to start rolling out to Android devices next week, beginning in the U.S. and coming to more countries "soon."

Periscope live broadcasts are now viewable directly in Twitter. Image source: Twitter.

Like Facebook, Twitter is also making live streaming on its platform easier. It recently enabled its live Periscope streaming to be viewable within Twitter, similar to Facebook Live. Periscope could be a particularly useful tool for the company as the smaller social network attempts to make it easier for users to connect and follow public figures.

Considering Facebook is successfully growing not just Facebook, but also Instagram, WhatsApp, Messenger, and Groups, too, Twitter would probably be wise to listen to Zuckerberg's advice. While Twitter is already moving in this direction, this area is probably worth even more emphasis if Zuckerberg says it is; he knows a thing or two from his experience with growing the world's largest social network.