I think my best bets for you are these folks:
Adrienne Reynolds, nearly 21. Former Ravenclaw. They probably knew each other in school. She works at the Daily Prophet but is now on kind of a probationary period because she ran a story she probably shouldn't have.
Simon Marek, 22. He went to Durmstrang but became a seeker for Puddlemere United until his former best friend framed him for murder and he ended up in Azkaban for several years. Recently released, he's trying to fly under the radar in hopes that people forgot his face.
Frank Longbottom, 24. Former Gryffindor, general troublemaker with a lot of secrets. He has a hidden side-job of taking polyjuice potion to look like other people and help those who have been wronged. For example, someone steals a priceless portrait and he's asked to find out where it is and/or get it back. But nobody close to him knows about his habits except for a few friends. TBH, it's kind of like that movie 'Hitch' if you've seen it, where people only know what he does because somebody he's helped suggests him to them. But I'm super fine with making up NPCs as a mutual contact of theirs if you should ever need him for that. Otherwise, he's not a super great friend but I figure he probably had lots of them in school.