To start I would put it on Craigslist , The Hull Truth and this forum. The Hull Truth doesn't have a huge trawler following BUT they do have lots of eyeball traffic which is always good. If no bites from those then you could try BoatTrader which will give you a basic ad for like $50 or so. I'm not a fan of BoatTrader but the price is right. Yacht World is probably the most used and known site but you'll need a broker to post it for you and that will cost at least 5% of the purchase price.
Why the jump from a 36' to a 40'? Doesn't seem like a big jump.
2005 Silverton 35 Motoryacht