Depending on your area try popular local newspapers with an adult ads section. These papers usually have websites that they let you advertise on. Not all of them have ad sections on their sites, but some do. You'll need to do a little digging here. Also try placing an ad here ECCIE, as well as getting listed on cityvibe.com, eros.com, menintransit.com, placing ads on bakpage.com etc. I myself get business from BP, eros, men in transit, cityvibe, date-check, preferred411 BUT that's me. Remember, your advertising success depends on you, your ad, your rates, location in which you advertise in, time of year, there are many factors that will effect the outcome of your ads. Another good source (I hear) was craigslist but they're long gone. Basically experiment with ad sites and remember not to get discourage if you don't see results at first... as the saying goes, if you don't succeed at first, try again! Also it doesn't hurt to ask around to other providers for good places to advertise on. Hope that helps.
try google...put in New York independent escorts in the search....check out the sites listed on the first page...they are usually best ones to advertise on
Since you're in NYC, I suggest the NY Times or Wall Street Journal. I'd suggest student newspapers, but having been a student once, I know they have no disposable income.
TheEroticReview, BigDoggie, and Escorts are probably the three biggest, most credible sites for escort service advertising and you can good review This site is from the US and Canada for popularity.