You will be able to contact the applicants who applied to your job post using the Message center.
Click on your avatar on the top right side of the page and choose My Jobs.
The My Jobs page will open, click on the Actions drop-down beside the job post, and click View applicants.
On the APPLICANTS page, you will see the list of applicants who applied to the job posting and you can contact them by clicking on the Actions drop-down and then choose Contact for each freelancer.
On the message pop up, enter your message, and click Send.