Could jinn find lost things, by knowing the Unseen?
The Jinn are different from humans both with the length of their probable lifetime and their overwhelming speed while in movement. Hence, they know many things that a man cannot know. So, it is possible for them to find things that are missing. However, those are already existent things that we cannot see or lost items. Essentially, those are not the Unseen things, which can only be known by God. For, in the Holy Quran, it is announced that some subjects that are related with the Unseen cannot be known by anyone but God.
For example, With Him are the keys to the Unseen; none knows them but He. And He knows whatever is on land and in the sea; and not a leaf falls but He knows it; and neither is there a grain in the dark layers of earth, nor anything green or dry, but is (recorded) in a Manifest Book. (Al-Anam Surah, 6:59) Both with the above-mentioned verse and with the following verse, it is stated that cases such as the future of the cosmos and humans; judgment day, death, fate, livelihood, character of the baby cannot be known by anyone. With God alone rests the knowledge of the Last Hour (when it will come). He sends down rain (just at the time and place He alone knows), and He alone knows what is in the wombs. No soul knows what it will reap tomorrow, and no soul knows in what place it will die. Surely God is All-Knowing, All-Aware. (Luqman Surah, 31:34)
Again in the Quran, while it is repeated that God, alone, knows the Unseen, it is also announced that He may inform some of the messengers whom He has chosen of the Unseen. (He alone is) the Knower of the Unseen (what lies beyond human perception), and He does not disclose His Unseen to anyone. Except to a Messenger whom He has chosen (and is well-pleased with – He informs him of the Unseen as much as He wills –); and He dispatches a watchful guard before him (between him and his audience) and a watchful guard behind him (between him and the origin of the Revelation); In order that He may establish that they (the Messengers) have for certain conveyed the messages of their Lord. He encompasses all that they have (of the Revelation), and He has recorded everything one by one. (Al-Jinn Surah, 72:26-28) Even though it is mentioned in the surah Al-Jinn, it is not stated that jinn may know the Unseen or God may inform them. Besides, there are verses that announce that jinn cannot know the Unseen. Then, when We executed Our decree for his death, nothing showed them (the jinn who had been laboring at the tasks he assigned to them) that he was dead, except that a termite had been gnawing away his staff (until it broke). Then when he fell to the ground, it became clear to the jinn that if they had known the Unseen, they would not have continued in the tormenting toil that humiliated them. (Saba Surah, 34:14)
Thence, we can briefly say that jinn cannot know the Unseen. Merely, things that are not equivalent to the Unseen or lost things which belong to this world can be known by them. Their speed, probable life, and size have great effects with this.