Salve! Welcome to the game, and to these boards! Many players started out w/ the free 4th ed - but 5th has much more support, both in fanbase and available supplements. (Just so you know.) 
There's a dedicated thread stickied above these threads for just this purpose (but, admittedly, it's not the most perused).
https://forum.atlas-games.com/t/help-finding-an-ars-group-or-advertising-one/1874/1
If you go to the main board index (nav from top-left of any page - "Board index") and scroll down, you'll find several play-by-post games currently run here, along w/ dedicated sub-forums for GM's and Players both to advertise. (Don't know about any 4th ed games atm one way or the other - you'd have to ask there).
Off this site, RPoL is one of the more active online pbp RP'ing sites, and has an active core of AM fans. Free, no spam, no scam. Be sure to specify 4th ed. http://rpol.net
Then there's always the Project Redcap site - fansite w/ links to all kinds of stuff, inc. on-line games.
http://www.redcap.org/page/overview
That should keep you busy until someone else chimes in.