finder
n.a person who discovers something that was lost or hidden. You use this word for someone who finds an object or even a new piece of information.
n.a person who discovers or locates something, whether by chance or through a deliberate search. Often used in the context of legal or social rules regarding lost property.
“The finder of the lost wallet returned it to the owner.”
“The museum offered a small reward to the finder of the ancient coin discovered in the field.”
“In many jurisdictions, the finder of lost property has a superior claim to the object against everyone except the rightful owner, provided they take reasonable steps to locate them.”
Commonly appears in the idiomatic phrase 'finders keepers'.
From Middle English findere. By surface analysis, find + -er.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.