Should update the readme to expain what this plugin does and how to use it?

Broken, since a player hasn't technically joined until they've passed the new player world.
Instructing them to ask guides for help is unhelpful since they cannot use chat in that world.

maybe a command:
/helper lookup aaldim

else if(args[0].equalsIgnoreCase("player")&&args.length>1){
                            OfflinePlayer p = Bukkit.getOfflinePlayer(args[0]);

^derp.

Also, you should convert those longs into something meaningful for the user

URLs are subject to change so should be configurable via the config.yml or something similar

Purely cosmetics, but informative text should be coloured, making it more distinguishable from normal chat.

There's a long chain of argument checks using only 'if' statements. This means every if statement will needlessly be checked regardless of which one is actually true.
Simply using 'else if' would improve efficiency.

A lot of the arguments do not return true on passing. This means that in many cases the logic will return the final false value (at the bottom of the method). This will then print the command usage or no perms message (thing) as if there was an input error, ignoring whether the command was successful or not.