If some of my friends join yahoo groups can i find there id?

Question

can i search in which group they are?

Answer 1

unless your friends in some manner display what groups they're in- no, generally speaking you cannot search by ID for who is a member of a group unless you're also a member of that group, and providing the member list is open.

Answer 2

you can join, find, or start a group here, http://groups.yahoo.com