What legal restrictions are there on advertising?
For Regulation Crowdfunding, you are only allowed to promote after your Form C is filed with the SEC. Oh, and never say the SEC has "approved" your offering. The SEC doesn't like that.
You are allowed to advertise any way you like - email, Facebook, shouting off the rooftops – whatever. However, all your advertisements must be limited to factual information (i.e. avoid saying you have the "best" cupcake shop in the world). Also, by law, all of your advertisements must include a link to your Wefunder profile.
If you haven't filed your Form C, you can ask people to "follow" your profile to show their support, but you cannot say something like: "We are going to fundraise on May 16th." Or: "As soon as we file with the SEC, we'll be raising at a $4 million valuation."
Check out the Legal Primer for more info.