We had an LTD a couple of months ago and now we just finished another 5-day campaign.
This picture is worth a thousand words. It’s the breakdown by source. As you can see, their email database is key.
You can promote your LTD to facebook groups and other communities, but I don’t think you’ll gonna reach that amount anytime soon.
Another important point is your product:
• do you have a virality build into your product? - the more users are using your product the more users you’ll get - then the answer is definitely GO FOR IT
• do you have high maintenance fees per user? then definitely NO