Tom Marvolo Riddle is a Legilimens. This means he is able to detect lies with very little effort and he can access every thought, image, and memory that crosses a person's mind while his attention is on them. He utilizes this ability as often as he can, despite it being considered "bad manners". It does not require much effort on his part, and with the constant use, it has become second nature to him. This subtle technique and use of Legilimency looks at the surface thoughts of a person, while leaving the person themselves oblivious to their mind being read. There's more to Legilimency as a whole, but this particular technique is the one Tom uses most often. (When it comes to using the others, Tom is able to do them, but they aren't utilized nearly as much, and I'll most likely talk it over with the other mun before he uses them.)
Of course, if the person is an Occlumens, is trained in another form of mental defense, or is simply like a one Bella Swan, Tom will not be able to access the person's mind, even for surface thoughts.
This post is for you to let me know who, or what, Tom does or doesn't have access to. If you don't put it on this post, I'll either go ahead and assume it's fair game, or try to play the muse as if it could go either way (although that isn't the easiest of things to do). I have no wish to become a metagamer, merely to stay true to Tom's character and play him as accurately as I can, which happens to include reading the minds of whoever he lays eyes on just because he can. Not the most polite thing to do, yes, but this is Lord Voldemort we're talking about.
And if you have any questions, feel free to ask. If you have any comments, feel free to leave them. Despite playing the Dark Lord, I'm a rather easy-going person. Any thoughts you might have are welcome. ♥