Hey guys,
I'm my sorority's new social chair for the year. And we haven't really been active lately so I've put myself up to the task of planning mixers with the fraternities. The problem is, the guys just aren't responding to me. And I know that guys do take longer to reply to things in general, but how should I ask them again without seeming annoying/desperate? I'm worried I won't be able to set anything up

Basically I Facebook messaged a few that I thought would forsure do something with us and no definitive response. Should I ask them differently? Or should I give them specific dates to choose from?
Help me out, other social chairs