If this is a single-member LLC, you do not have to report it on your personal federal tax return - when there isn't any income or expenses, there isn't anything to report (this is the equivalent of telling the IRS and the state that "you made and spent zero").
If this is not a single-member LLC, you don't have to file a federal business return - if no income, deductions or credits are being reported or claimed, there is no requirement to file a federal return
Some states, however, require LLCs to file a business return (partnership or corporate) whether or not you have any income or expenses. For example, CA and NY require you to file a business return just because of being registered (formed) in their state.
