A group of teenagers decide/decides to move forward

[davefreud]

The sentence begins with," A group of teenagers". Which is correct?
A group of teenagers DECIDE to move forward .
A group of teenagers DECIDES to move forward

 

[5jj]

We prefer to think of group nouns as plural in BrE; most of us would use 'decide'.

 

[emsr2d2]

The I want to write a sentence that begins with, no comma here "A group of teenagers". Which of the following is correct?
1. A group of teenagers DECIDE to move forward.
2. A group of teenagers DECIDES to move forward.

Note my corrections above.

If you start with "The sentence", it suggests we already know what sentence you're talking about. We don't.
Don't put a space after opening quotation marks.
Don't put a space before a full stop.
When you give us more than one sentence to look at, please number them.

Note that I've changed your thread title. Titles should be unique, relevant only to your thread and contain some/all of the sentence you're asking us to look at.

 

[Tarheel]

This is one way British English and American English are different. Americans see a group as a unit and grammatically singular.