The Office of the Grand Ayatullah Khamenei (may Allah prolong his life):
In the case inquired, if you have no hope in finding the owner, and the value of the property is more than 12.6 chickpeas of coined silver, it is an obligatory precaution to give the value of the property in charity on behalf of the owner before using it.
The Office of the Grand Ayatullah Sistani (may Allah prolong his life):
You will have to announce the property has been found for a year.
The Office of the Grand Ayatullah Makarem Shirazi (may Allah prolong his life):
You have to try to find the owner for a year, in the process, if you ever lose hope in finding him/her, you can give the property to a poor person in charity on behalf of the owner.
The Office of the Grand Ayatullah Safi Golpaygani (may Allah prolong his life):
Please refer to issue number 2573 of my risalah for the answer.
The Office of Ayatullah Mahdi Hadavi Tehrani (may Allah prolong his life):
1- It is makruh to pick up any property that is on the ground.
2- If one finds some property and picks it up, he has to announce this for a year until the owner is found. After this period, he can own the property for himself, although if the owner shows up and asks for it, the finder will be liable. Of course, it is better to give that property in charity on behalf of the owner after the one year, and if the owner shows up after a year and doesn’t give consent to the charity, the finder must pay him the value of the property and the charity will count as the finder’s.
3- If after finding property and announcing for a while, one becomes hopeless in finding the owner, he can act according to the ruling mentioned above, even if the one year hasn’t passed.