HI @Despina0
Sorry to hear about that situation. This is one of the less pleasant types of experiences that one can have when hosting. It is a rare occurrence, but always possible, that hosts' property will go missing. Sometimes guests move things about, sometimes they accidentally throw something out, sometimes they accidentally pack something up in their luggage, and on rare occasions, they steal host's property.
Here is another post on this type of situation: https://community.airbnb.com/t5/Host-Circle/Item-missing-from-hosts-house-after-guests-left-what-to-...
Basically, the general rule for loss/damages involved in hosting is, that unless you know for sure that loss/damage was caused by a certain guest or group of guests, it is not fair to bill them for that, and even if you attempt to do so, you may not be successful. Sometimes, a host will notice something is missing, but it may have been missing for some time, and was missing even before the most recent guest arrived. So it could have been taken by a guest several reservations in the past.
As well, Airbnb is more likely to reimburse you for actual damages that you have evidence of (eg photographs), than for items missing, in which case, it is a "he said/she said" situation where host tells one story, guest tells another story, and Airbnb doesn't know whom to believe.
I strongly suggest that hosts do not leave any items which have significant personal/sentimental value, in areas that guests have access to, because any of those could potentially go missing. Keep your sentimental items in your own space, or locked up, and in the guest areas, keep only those items which would not leave you inconsolable or feeling bereft if lost.
IF you are quite sure an item was there prior to the arrival of the most recent guests, you could try to bill them for it via the resolution center at www.airbnb.com/resolutions, however, if guest already states that they are not responsible for this, they are likely to decline the resolution request bill for payment. Airbnb could possibly mediate and decide in your favor, but I think this is a less likely outcome, in a situation with two different stories and no "evidence."
If the missing item is of not much monetary value, it would not do much good to submit a claim on the guest's security deposit or a resolution center request, because you can only ask for reimbursement for actual value, not for sentimental value.
So in this case I think if the guest is not cooperative, and does not reply, or says they know nothing about this, I would take this as a lesson learned, and from now on not put items of personal value in areas guest has access to, and then try to let this go.
