These types of promotions can be fun, but can also get tricky. There are a few things to consider. First, your regulator has rules prohibiting lotteries. For example, the FDIC's version defines a lottery when three or more persons "advance money or credit to another in exchange for the possibility or expectation that one or more but not all of the participants (the "winners") will receive by reason of their advances more than the amounts they have advanced...". Based on what you provided, it doesn't appear that you have an entry fee (i.e. requirement to advance money or credit), so this doesn't appear to be a "lottery" by definition.
As this contest appears to pass that first test, you will now need to look at your state laws. It is my understanding that some states have pretty strict contest and disclosure requirements to ensure your contest is a "sweepstakes" and not a lottery, so this is where you will probably want to involve legal counsel to ensure you comply with your state laws, including the creation of your sweepstakes disclosures.
Adam Witmer, CRCM
All statements are my opinion, not those of my employer, and should not be taken as legal advice.www.compliancecohort.com