I have tried all the ways I can think of to promote it: Google AdWords, Facebook Ads, StumbleUpon, AddThis links, Live Twitter stream on the homepage, Android App, HackerNews, Reddit.
I am still having trouble grasping a constant stream of visitors. Any ideas on how to promote it? Any tips are much appreciated, thanks!
What I recommend you do instead is actually sell your product to the insurance industry (perhaps as a white-label product) for their customers. It provides direct value to them as they can use it to reduce fraudulent claims and manage accounts more easily as well a providing a value-add for their service.
1. I understand what the service is based on your comment above and reading through the website, but it is not completely evident to me at first glance when visiting the site. When I get to the site, the first thing that jumps out at me is to enter the tag # or serial # of an item I found. If you are trying to draw users in, I would suggest focusing more on getting people to signup and enter their things. Maybe put a link for people who find something and want to try and track down the owner.
2. There is no privacy policy or TOS that I could find. If I am going to enter my info I want to know you are going to keep it private.
3. While I could care less, some people may have a concern having a link between items they own and their Facebook account. Facebook doesn't have a good privacy record, and it would concern me that they could now know specific items I own and target advertisers to me based on that info.
4. You are looking for a constant stream of visitors, but the site is more of a signup once, enter your items, and never visit again. There is nothing to engage me once I have signed up and entered my items. Not sure what you could do here, but a couple of ideas may include (a) alerting me when product recalls, updates, upgrades, etc... are available from the manufacturer for a specific item; (b) creating a forum of users with the same products to discuss topics related to the product. Of course all of these would require some opt-in notifications to the user, but could enhance user engagement to some extent. Another idea, would be to allow the user to report an item stolen and automatically search sites like eBay and/or craigslist for matching items that recently were listed for sale in the user's area.
Good luck though, I really do like the idea. I have had things stolen from my car and home and a service like this would have been very helpful in filling out the police reports.
I'd say your best bet is getting reviewed by some high traffic blogs.