Look who he was spotted out with= Look whom he was seen going out with

If you (or especially a celebrity or well-known person) were "spotted out with someone," it means you were "seen in public with someone." Since you usually hear it used this way in tabloids or sensationalistic journalism, it implies that the people in question didn't wish to be noticed. "To spot" doesn't always have a negative connotation though. While it's true that you might want to spot your enemies before they spot you, you might also spot your friend in a crowd, spot a great parking space or spot an empty seat on the bus, all of which would probably make you quite happy. When in doubt, substitute the correct form of "see" for "spot," and you'll still be making perfect sense.

We don't say it that way in American English, but he was probably seen with someone who is either a questionable person, a famous person, an infamous person, or somebody he should not have been seen with. For someone to say "look who he was seen with...." it was something to talk about. That's my guess.

Look who he was spotted out with ^ That sounds like a gossip magazine. It means a man was seen with someone. "Spotted" means seen in an odd way. "out with" means doing an activity with someone. The activity could be shopping, having dinner in a restaurant etc.

Somebody spotted him= Somebody saw him But we sometimes say 'spotted' when we see something unusual Not unusual example- I spotted this great place for a picnic yesterday while I was driving in my car. Unusual example- I spotted Brian downtown yesterday and guess who he was with! He was with Susan, the girl he said he didn't like.