This is something we are actively considering and planning to do more of at Giving What We Can! Finding the right people who may be well aligned with our messaging and goals, and have an audience that would resonate too is key. If anyone has appropriate suggestions, please feel free to email me!

I think this is a great idea and -- as a newish member here -- am surprised it's never been attempted.

Some additional thoughts...

1.

While the terms "celebrity" and "influencer" can sometimes be used interchangeably (and crossover does exist), the marketing world often views the two personas as distinct. There has been some research on the differences between the "celebrity endorsement" and "influencer recommendation" with influencers often delivering better results. This is  supported by micro influencers often getting higher engagement rates than much larger influencers and celebrities.

You can use this tool to not only explore the engagement rates of different Instagram influencers, but also the cost of partnerships. Here's a quick comparison between Justin Bieber and The Physics Girl :

Justin Bieber

• Followers: 233M followers
• Posts: 7,122 posts
• Estimated Cost Per Post: $463,948 - $773,246
• Engagement Rate: 0.18%

The Physics Girl

• Followers: 146,489
• Posts: 716
• Estimated Cost Per Post: $439.89 - $733.15
• Engagement Rate: 3.51%

Even with the lower engagement rate, you're still  going to get massive exposure through Justin Bieber. However, audience match and behavior should  still  be considered when estimating CR (conversion rate):

• Is the cause/message likely to resonate with the celebrity or influencer's audience?
• Are members of the audience likely to take action around the cause/message?

2.

This idea of "niching down" can also be applied to the cause area or organization. In other words, instead of a celebrity or influencer endorsing EA,  they could instead promote specific EA-related causes or charities e.g. global poverty and health or Giving What We Can, AI alignment or The Future of Life Institute, etc. EA, as a cause area and philosophy, has a bit of a learning curve attached and some/many people might not want to put in the work -- losing them as potential advocates along the way.

On the other hand, a specific cause or charity is likely easier for the uninitiated to understand and support. Some examples of messaging (celebrity voice)...

• EA - I support Effective Altruism -- a social movement and philosophy focused on maximizing the good you can do in your career, projects, and other life decisions. Learn more and see how you can get involved as well! (link in bio)
• Global poverty and health - I believe helping people in low-income countries is the best way to focus my philanthropic efforts. See why I give and how you can get involved as well! (link in bio)
• Giving What We Can - I just took a pledge to give 10% of my income to help fight global poverty. Find out how you can get involved as well! (link in bio)

Each of those blurbs could be punched up, but I tried to keep the last lines as close as possible for a more apples-to-apples comparison (subjective as that may be). There are pros and cons to each but, generally, the more targeted, clearer, and specific a message, the higher its engagement and CTR (click-through rate). Still, you'd want to test variations across audiences, cause areas, and CTAs (calls to action).

All of that said, I think celebrities/influencers promoting EA would be mostly good. My guess is that going more granular with aligned influencer audiences would produce better quality and longer lasting results.

I both think this is 'obviously' good in the expected value sense that's going to be undervalued by most people, and likely to be cringe if done by many or at least some fraction of people who try to cram some propaganda down someone's throat.

"Have you heard the good word of effective altruism?" click

Maybe I'd point at an ethos more like 'find scenes you vibe in, befriend and converse with powerful people in those scenes, and they will naturally receive your values through osmosis'. 

Maybe most people here should just focus on engaging in forthright exchange with each other and others you find in the world, and this will naturally tend to exert a memetic gravity that pulls people in rather than trying to push on others.

It could be more effective to engage celebrities who've already supported EA or parts of EA to do so more publicly and often, or otherwise get more involved.

We already have celebrities who've narrated parts of Peter Singer's The Life You Can Save:

The chapters of the audiobook are read by celebrities, including Paul Simon, Kristen Bell, Stephen Fry, Natalia Vodianova, Shabana Azmi, and Nicholas D’Agosto.

Joseph Gordon-Levitt was on a panel at EA Global.

Cate Blanchett was reading The Precipice.

There are lots of celebrities who care about animal protection, and we could approach them about effective animal advocacy.