Social media has transformed electoral politics and allows campaigns to micro-target supporters. However, little is known about the effectiveness of political ads on social media, particularly those that appeal for money. We study the fundraising effects of ad campaigns sponsored by a well-funded Super PAC, The Lincoln Project. Our model includes 100s of millions of ad impressions targeting Facebook users in the 50 states, plus D.C., over 308 days in 2020. We coded ads for tone and fundraising appeals and find that the most effective ads are those that directly appeal for money, while ads that use negativity are associated with a small, positive effect. Ads that include both negativity and fundraising appeals are associated with the most money: each impression yields an additional $0.52 in itemized donations (campaign contributions). The results confirm what previous research on campaign giving has found— people tend to give money to campaigns when they are asked to—and show how digital advertising influences political behavior.