Speaking from a not so good experience I firmly believe that a project without whitepaper is definitely a scam. I almost but thankfully did not invest a single penny on that scam project. Surprisingly they did raise an amount considering their ads and website looked like it was made by a 1st grader. If I'm not mistaken they raised less than 1Eth. Going back to the topic though, I don't want to generalize but how can the investors understand what a project is about if there's no whitepaper to read, right? Better stay safe and just go with the ones with whitepaper (almost all projects have one, anyway) but it still doesn't guarantee if they are legit.