You can find neighbors by asking in the #nodesharing channel on the official IOTA Slack.
If you are not already a member, you can sign up here: http://slack.iota.org/
Within the GUI, select ‘Tools -> Edit Server Configuration’ to add neighbours.
In the text box below ‘Neighboring Nodes’ you need to add a different node to each line. Be careful not to add an incorrect character or any extra space.
It is recommended that you have between 7 and 9 neighbours. All must add your node in return as, if they do not add you, you will not be able to connect to them. Having more than 9 neighbours is highly advised against, as it is harming the network.
Click ‘Save’ and the GUI wallet will restart.
It is important to note that having a static IP is required to use IOTA for any length of time. If you have a dynamic IP it will change roughly every 8 hours, meaning you will need to periodically ask all of your neighbors to update your IP; this is obviously not sustainable.
You can use a service such as noip.com to get a static IP - see our guide here for instructions: http://iotasupport.com/staticip.shtml