SINGLE MEMBER LLC (SMLLC)
A single LLC is considered a Disregarded Entity and defaults to a Schedule C (Profit or Loss From Business) or Schedule F (Profit and Loss from Farming) as applicable, thus, you do NOT have to include it on your 1040 if there is NO ACTIVITY.  One thing that needs to be clarified, having expenses for the operation of the business despite having little to no income is regarded as Business Activity and the appropriate tax forms should be filed as such.

MULTI MEMEBER LLC and S-Corporations
A Multi-Member LLC , by default, is regarded as a Partnership and files IRS Form 1065, unless an election is made to be regarded as an S-Corporation by filing IRS Form 2553.

Per IRS, a domestic partnership must file an information return, unless it neither receives gross income nor pays or incurs any amount treated as a deduction or credit for federal income tax purposes.

Partnerships Filing Requirement - IRS 

However, an S-Corporation that has no expenses, depreciation, assets, carryforwards, etc., MUST still file a Tax Return (IRS Form 1120-S) regardless of activity as long as the S-Corporation Election remains in effect.

The penalty for NOT filing the S-Corporation Tax Return is $235 for each person who was a shareholder any time during the tax year, for each month or part of a month that the return was filed late, for up to 12 months.
U.S. Income Tax Return for an S Corporation

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