I am pretty sure exitround is inactive and don't think it is the best match for app sales.

Flippa, as Lee stated, is a great place to list your app. Also is Fliptopia. https://www.fliptopia.com

The latter is focused on apps and has their own built-in escrow service, which is usually efficient. Flippa users usually use escrow.com, the last time I checked. I have done several buy and sell side transactions, using both Flippa and Fliptopia.

Good luck,
Jeremy