Not quite, you'd need to look attractive (not necessarily poor).

Seriously, why are you asking about Karaoke places? Are you travelling alone?

Both jib71 and myself have referred to the ubiquitous karaoke booths Big Echo is a chain you'll see everywhere, often a multi-storey building with booths like little hotel rooms on every floor. Once you pay for your cell you can telephone for drinks and snacks, so they are like private rooms in a pub, just sound proofed to help everyone who isn't in with you have a good time. Some of the rooms have whacky interior decor and themes.
Hiring one of these would be an awfully sad and lonely thing to do on your own... but there are plenty of people who do just this.

There are probably 'normal' bars that have public karaoke (this might be what you are used to and are expecting to find). If there are, I've never been to one, and if I did stumble into one I'd likely bash my shins in my haste to stumble out, although it could be worse, it could be somewhere with live Jazz (shudder). The only place with a karaoke stage I've been to was in a Hostess bar.
Good luck finding someone who knows where to find one of these in Tokyo, even better luck in finding someone who'll actually admit they know!