For Facebook and Twitter, directly contact the owner of the account, explain who you are and ask that they transfer the account to you. If they do not cooperate, send us a message and we can help to facilitate a transfer.
For URLs, ask members of your community and team if they have purchased the URL. If not, directly contact the URL's owner (try a WHOIS lookup to obtain their contact information) and ask that they transfer the URL to you. If they are unresponsive, send us a message and we can help to facilitate a transfer.