@salima,
If you know their email addresses you can use the My Friends tab in the menu bar above. Click the Add Friends tab and type in the full email address of a person you seek.
If they are registered here, their user name will be displayed and they will automatically be added to your "Following" list on your profile page.
The drawback is that you do have to know their email address before this feature is useful.
If you had a mailing list for members of one of your groups on the old philosophy forum, you can use the utility button on the Add Friends form to import your address list so you can search for them here and add them to your Following list.