OK. We need to have these steps completed before we can determine any other causes.

1. Disable any firewall or security features on your router - http://portforward.com/english/routers/firewalling/routerindex.htm -

2. Set port forwarding on your router to the IP address of your Xbox 360. This game uses port 3074 (UDP/TCP)

    Additionally Xbox Live requires ports 80, 53 (TCP) and 88, 53 (UDP).

** www.portforward.com can be of use when assigning ports also**

3. Place your Xbox 360 into the DMZ of your router

http://www.question-defense.com/2010/02/13/how-to-configure-a-static-ip-on-a-xbo x-360-located-on-your-local-network

This link below is only if your having connection problems once assigning the static IP

http://portforward.com/networking/staticip-xbox360.htm

NOTE: If setting port forwarding or DMZ helps your connection issue, you may want to assign your Xbox 360 a static IP address within your home network. This can help to ensure that the configurations you made do not need to be done again.

NOTE: Many broadband internet modems are coming with routing capabilities built in. Please contact your internet service provider to determine if your internet modem has an integrated router. If it does, they should be able to assist you with the steps above for setting up your router.

4. If all fail, disconnect your router and try the game. If it works regularly at this point something about your router may not be completely compatible with the specific needs of this game. Check with your router manufacturer and Microsoft's Xbox Live Networking Help page for additional steps that may need to be done to resolve the issue you are having.

http://support.xbox.com/support/en/us/nxe/xboxlive/troubleshooting/NetworkHelp.a spx

5. You can also check the following link to verify that you have an Xbox Live compatible router.

http://support.xbox.com/support/en/us/nxe/xboxlive/getconnected/CompatibleNetwor kEquipment/CompatibleNetworkingEquipment.aspx

6. Once you have verified that your network setup is not the cause of the issue, try the following

    - Try connecting to a different server. Some servers may have other players connected to them that you do not have an optimal connection with. In most games this is accomplished by backing out to the main menu and then selecting multiplayer again. From there you can try connecting to another online game.

    - Run the Xbox Network Self Test to see how strong your NAT is currently set to. Turn on your Xbox 360 without a disc inside and go to "My Xbox", select "System Settings"-> "Network Settings" then choose "Test Xbox Live Connection" and let the test run. Once the test is completed you will be notified if there is an issue with your connection. If you select "More Info" you will be given information about your NAT type and some steps to resolve any issues with your connection.

^MS

Update: Tried again this afternoon. Same problem - no matches to be found anywhere.

BUT! I disabled DLC and only played the original maps ('back' button on the controler when connected to Xbox Live in multiplayer) and suddenly everything worked fine. Every game mode, 45-50 matches found.

The only DLC I have so far is 1 and 4, and all of this started after buying DLC4. Very annoyed.

I have dlc 1 and 2 and have had this issue for ages. Thought it was to do with peeps leaving the game and playing black ops 2 or the new maps for mm3. However I do distinctly remember in hind sight after reading this post that everything went weird after I installed dlc 2. I cant find as many games and the games that I do get to play took ages to find. I have deleted dlc 2 and will test. I will report my results. BTW my NAT has always been open but I decided wtf I'll forward the required ports for xbox live in my Virgin Super Hub to see if that would help but the issue remained.

I would hate to think that the way to fix this is to purchase the remaining map packs. I think that if that is the case I will be posting and blogging all over the web that the fix for this is that users are being forced into forking out yet more money to be able to play this game instead of the developers fixing its match making capabilities.

Thanks for the info guys, could have saved everyone a lot of time if Activision or whoever just said that months ago. The small 2week's I had playing dlc 4 maps were a fluke or just to encourage me to buy 2 and 3 before it stopped finding games?  . 2 map purchases wasted, shame as parish was an amazing map with an mp7 and claymores.