I need some ideas on promoting a social media platform online

Try getting someone famous (in relevance to your target/desired audience) to post that they are on your platform (be sure to make sure that the platform works and gives value before approaching them - otherwise nothing you do will work).
p.s.: before launching, did you actually check that there was a need for this platform (no offence, but this is crucial to know before)?
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Hi there -

In my experience it comes down to your audience's perception of the value of your product... is it worth giving you their email address (which I believe is what you are referring to when you say "sign up" and that there is no fee)

Sometimes audiences need something free and tangible first - like a free digital product or download. Other people need an experience to interact with other people. And many people are motivated by a deadline.

Why don't you try this... create a virtual event on the social networking platform for a date and time that fits your ideal audience's schedule. Then include that event in all the comments, connections, memes, Q&As, blogs, etc. Drive interest in the event on your platform. Put a deadline in the sign up messages. However, your audience can't access the event without signing up for your social networking platform. Also let them know that if they sign up by your deadline, they will receive a free digital product or something your audience will consider valuable. Lastly during the virtual event, take screen shots, encourage folks to post and participate. For your next outreach campaign (which is what you have been doing to increase traffic and usage) utilize the images and details from the virtual event to motivate and inspire other folks to sign up.

If you have any follow-up questions, feel free to schedule a call with me.

Best of luck!
Leslie Pankowski