探す and 捜す: looking for something wanted or lost
Compare looking for a suitable item with searching for something lost, without treating overlapping spellings as absolute rules.
Look for something suitable
駅の近くで部屋を探しています。 says that someone is looking for a room near the station. 探す, read さがす, is used when seeking something that meets a need.
プレゼントにする本を探しました。 says that someone looked for a book to give as a present. It does not require a particular book to have been selected and lost.
Search for something missing
落とした鍵を捜しています。 means that someone is searching for keys they dropped. 捜す is also read さがす and suits searching for a particular missing item.
迷子になった犬をみんなで捜しました。 says that everyone searched for the lost dog. 捜した describes searching and does not establish that the dog was found.
Spelling tendencies and finding
探す can also be used for lost objects, so 鍵を探す is not automatically wrong. Treat the spelling distinction as a tendency and read the object and situation first.
一時間捜しましたが、見つかりませんでした。 means that someone searched for an hour but did not find it. Separating searching from finding prevents reading a past search as a success.
Does 犬を捜しました necessarily mean that the dog was found?
Show the answer and why
No. It reports the act of searching. A result such as 見つかりました is needed to establish finding.