Download PsLoggedOn. I quote:

<b>PsLoggedOn</b> is an applet that displays both the locally logged on users and users logged on via resources for either the
 local computer, or a remote one. If you specify a user name instead of a computer,
 <b>PsLoggedOn</b> searches the computers in the network neighborhood and tells you if the user is currently logged on.

<b>PsLoggedOn</b>'s definition of a locally logged on user is one that has their profile loaded into the Registry,
 so <b>PsLoggedOn</b> determines who is logged on by scanning the keys under the <b>HKEY_USERS</b> key.
 For each key that has a name that is a user SID (security Identifier),
 <b>PsLoggedOn</b> looks up the corresponding user name and displays it. To determine who is logged onto a computer via resource shares,
 <b>PsLoggedOn</b> uses the <b>NetSessionEnum API</b>. Note that <b>PsLoggedOn</b> will show you as logged on via resource share to remote computers
 that you query because a logon is required for <b>PsLoggedOn</b> to access the Registry of a remote system.

Just copy <b>PsLoggedOn</b> onto your executable path, and type <b>psloggedon</b>.

usage: <b>psloggedon \[-?\] \[-l\] \[-x\] \[\\computername | username\]</b>
 <b>-?</b> Displays the supported options and the units of measurement used for output values.
 <b>-l</b> Shows only local logons instead of both local and network resource logons.
 <b>-x</b> Don't show logon times.
 <b>\\computername</b> Specifies the name of the computer for which to list logon information.
 <b>username</b> If you specify a user name <b>PsLoggedOn</b> searches the network for computers to which that user is logged on.
          This is useful if you want to ensure that a particular user is not logged on when you are about to change their
          user profile configuration.