Rather than following up constantly, I would suggest trying to get other investors onboard, keeping the investors who ghosted you up to date with the progress. Sometimes there’s a signaling issue where the investor wants to see other well-known names before committing. If you FUP constantly, you may put yourself in a situation where you get a straight “no”, you could still keep the optionality. Momentum is important, but it’s also important to be strategic in the fundraise process so you don’t shut any doors!

I wouldn't put too much emphasis on the ghost investors and move on. Every investor is in a specific place at the time of your deal (already evaluating something else or just invested somewhere etc) and hence didn't respond. I make it a practice to at least respond to any investors who send me direct DMs as a courtesy.