What Phil said is best for approaching something/someone in a normal manner. But if you're up to no good or if you simply want to surprise someone, you might sneak up on him. 😈

~He sneaked up on the cat.

*You might hear 'snuck up' on the cat, but it's not accepted as correct in come circles. However, it is in the dictionary.

~Sometimes I sneak up on my husband just to see him jump. 😉

Dictionaries:

to get very near someone before they notice you

sneak up on: <em>Don’t sneak up on me like that!</em>

More formally, we can say that he approached the cat. More informally, we can say that he got close to the cat.

Thank you guys! Great answers! ;)

the man moved near the cat

The man moved closely to the cat.