Good questions, but think it through.
For argument's sake, let's assume the alien species is like us, looking at other stars for signs of life.
A planet which has developed life in parallel with the way Earth has would be identifiable as life-bearing from quite a long way away, because free oxygen in an atmosphere could only come from ongoing photosynthesis. We are close to being able to detect it in exoplanets up a few thousand light years. Needless to say, nothing has been found so far.
But if our aliens had FTL capability, then depending on its maximum warp factor, just like us they'd probably go to other stars simply because they could, for pure exploration. That way, they might well stumble upon us without previously knowing we're here. It's like early human explorers setting off into the unknown, with the major difference that the aliens know where they're going and how long it would take, though still without knowing what they'd find when they get there.
Free oxygen is the only technique we know of for detecting life in other star systems, and even that would not find those which didn't invent photosynthesis.
Civilizations like ours could only be detected by structured radio emissions. The trouble with that is the signals soon get swamped by background noise, and we could only detect ourselves at about a lightyear or less, so not even from the nearest star. Even in theory, with ideally sensitive equipment, we couldn't improve that by more than a lightyear or so. Also, despite our use of radio increasing hugely, its efficiency is improving such that the strength of our radio 'signature' is diminishing all the time. We only need a few watts of power these days to send a signal around the world. A few decades ago it was kilowatts. So we've probably already passed our peak of radio 'leakage'.
A directed radio signal, like that part of the Arecibo SETI project, is different. That's a narrow beam with the power to blast through the noise and reach across the Galaxy. But because it's narrow, looking for a signal from another star means either scanning the cosmos in a pattern search hoping for a coincidental hit (look up the 'WOW!' signal); or examining every star one at a time.