How do I send a group SMS with google hangouts? I have a Samsung Galaxy S4 on Verizon if that matters.  Thanks!
In Hangouts start a new conversation by going to the Messages tab and pressing on the "+" button on the top-right.
Select the first contact.  This should open the Hangout conversation screen:

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Tap the "Anyone else?" button next to the first participant on the top row.  This brings up the "New group conversation" screen:

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Add more contacts you wish to be included in the group conversation by tapping on their name, or typing in their name:

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Press the OK button.  This opens up the actual group conversation with all the selected participants.  You should see "Send to group" in the typing area, signifying that you are starting a group Hangout:

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You can also turn an existing single-participant hangout into a group chat.  Just open the existing chat, tap on Menu button, select "New group conversation" and continue on from step 3 above.

Now messages you send and receive will be shared with all participants.