Community Moderator Alumni are previous members of the Moderation Team, which ensures conversations are friendly, factual, and on-topic. Moderators are here to answer questions, escalate bugs, and make sure your voice is heard by the larger Fitbit team. Learn more
Oh! sounds too bad that your One got lost @PaulineWW. 
Since this was recently, and if your tracker still have battery, I believe that we have chances to find it. So take a look of this post which has tips to locate a lost Fitbit. If after that you can't locate your tracker, please get in touch with Fitbit Support to get further assistance.
Cross your fingers! I'm pretty sure you will find your tracker. 
Best Answer
Fitbit Product Experts Alumni are retired members of the Fitbit Product Expert Program. Learn more
Hello @BunnyOye,
Welcome to the community, though sorry that it's under these circumstances...
Hopefully, you sync your Fitbit with your phone, it'll give you a few more options for narrowing your search.
My phone (Microsoft Lumia 950) has a 'gadgets' app that will tell me when and where a device was connected, it looks like this:
I can tap on it and even ask for directions to that last location.
Barring that you can still get hints as to where it might be:
First, look at your dashboard towards the top. Next to the date, it'll tell you the time of your last sync. This is likely the last time you definitely had it on you. Do you remember where you might've been at that time? You can cross-reference that time with times of phone calls and text messages to help trigger your memory.
Next, look at your step/floor activity for that day on your activities page. Specifically, cross-reference the time of your step/floor activity with the time of your last sync.
For instance, if the time of your last sync was 12:30pm, but your last step activity was at 12:10pm, then that means that you were not moving for 20 minutes before you lost it. Any chance you dropped it at a booth in the restaurant?
If your last sync was at 1:30pm and you had steps up until that moment, where you at a particular store at the time (look at your receipts)?
Lastly, I recommend labeling your Fitbit. I've labeled mine (and friends') and we've had four happy returns. I use a Brother p-touch labeler and it looks like this:
I think most people would return it if they knew who to contact.
I hope this helps.
Best Answer