Here you will find a list of places you can go to debate theology. Along with each reference is a short review rating how good the debates and moderation are.
I would advise against arguing theology over Facebook. Facebook is best used to increase your social circle not decrease it. That will help you more in your efforts than anything else. Build the right kind of friends and not the wrong kind of enemies!
Link: DebateAChristian on Reddit
Appears to be a medium quality debate site, suitable for casual debates and questions. Here are a few example debates I pulled which I feel are representative of the forum:
As you can see you do get the occasional “It only seems contradictory because you're misreading Ezekiel.” but otherwise the debates are respectful and people do attempt to give serious answers. The occasional concession is given. Difficult subjects seem to be treated fairly with respect to upvoting. Rating: 4/5.
The difference between 4/5 and 5/5 is huge. They would need to have more people who followed more closely with modern apologetics. More people who were willing to put their name and reputation on the line behind their statements. Perhaps, as some sort of forum of professional apologists. In short the forum itself lacks credibility because it does not make any claim to credibility. It is merely a public forum for debate.
Link: ChristianDebate on Reddit
Quality unknown. It's a private forum and I have not investigated it yet. Unrated.
Homepage is http://www.acrity.org/
You will need an IRC client such as HexChat to access this service. Select a DALNET server and join channel #ChristianDebate when you are connected.
This is a low quality debate platform with little if any credibility in apologetics. Debates will often degrade into logical dishonesty. If your case is made with scriptural support you will often be accused of spiritual blindness or having a veil over your eyes. If ultimately your case cannot be dealt with you will be accused of lying, trolling, or making things personal, and you will be threatened with a kick/ban if you do not apologize for your 'antagonism'. Don't bother appealing to Sara (or any of the channel founders), they do not answer their mails and are most often the people responsible for these abuses anyways.
In truth many of the people here are not really interested in debate at all, but in out-talking people. The moderators themselves do not follow any ground rules of debate. A frequent tactic is to claim that they have won the debate and then simply refuse to talk to you anymore. Very few times will you ever see any source for the claims which are made on the channel, and often they will be gross misquotes. As an example I have seen people quote Genesis 1:2 to prove that God didn't create the heavens and the earth (obviously, skipping over Genesis 1:1).
People will engage you, and you will sometimes get a decent conversation, as long as you don't get too close to something they can't answer. At that point the appeals to authority, power-tripping, name calling and ad-hominem will begin. Keep your wits about you and don't take this channel too seriously, they don't take themselves seriously as a credible debate platform so there's no reason you should either.
As a final warning, never engage the ops in debate. It's possible but difficult. How you go about evading their trolling and baiting is up to you. Rating: 3/10
More Information on Dalnet debate channels here.