I shoot pros when I can but living where I am they not always available.

I advertise for paid shoots for newbies and am annoyed by the the number of 'models' that once they get an agreement from me to do a shoot they stop. There are not canceling as we did not set a date/time but at the point where I would agree to a shoot. It seems that my approval of them as a model is all they need.
I've been using some local Facebook groups and gotten several in the past week.

For me Instagram works better then Facebook.

I'm pretty sure a lot of that happens here on MM, too.
There are several models that seem they'd like to get a gig, but don't reply to legitimate offers...
... and months or years go by and they still have the same (usually crappy) photos posted that they originally posted.

I just block 'em (so that I don't make the mistake of asking them again) and move on.

I used to run into that on here quite a bit. I think there were a lot of models who created MM profiles simply so they could tell their friends they were models.   I also think for some new models, actually scheduling a shoot with someone they’ve never met is when they get cold feet.

Facebook is not the least bit reliable. One of the first shoots I did I made the mistake of agreeing to a shoot with a "model" (quote/unquote) who had an  aerobics looking shot on a website. As soon as she saw me at the meeting location she was a total deadpan who seemed to not want to get out of her car even. Not worried or distrustful ,  just disinterested . If it ever happens to you I would suggest handing the subject a few bucks to cover gas expense and send her on her way. In my case I stayed and eventually I was able to get a few sparks out of her  to take one or two photos that were not too bad. ( I stayed because this was my first opportunity to do a "one on one" shoot with a model and I had actually given up a group shoot involving motorcycles at a Harley Davidsons to shoot with this gal .What a bad mistake).On a later shoot when I met up with a different "model" (quote/unquote) the model she seemed to only want to shoot 2 or 3 specific poses she thought up with little input or concentration  . She wanted the images for facebook and friends and told me after we met that she had to leave in an hour. Bottom line - forget facebook - they are not trying to be serious models. Ask questions about why she needs the shots and "touch base" a few days ahead of the shoot as to what you both hope to accomplish . I have not seen either of the two models on social sites or  sites all about photography modeling . For serious shoots try "Meetup" for a start , or "model mayhem", or "model management". I am not sure about other sites such as Instagram. Seems they have serious models on it but at the same time if you are on some of these sites they may want you to switch to another site. Sometimes they are serious and sometimes up to no good.Go to sites dedicated to serious photography .

Any Big City  Model with Potential ( to become Pro ) probably has dozens of requests from Photographers

For some Modelling is more Fantasy than reality - but Others are more serious

I think for those that are more Serious about Modelling - A Photographer needs to stand out in some way for them to really be interested .... For Me I try to cover all the bases - Good Work . Good Reputation ..A bit of Cash .and some Real World Connections to Agencys and Major Fashion Events ....And all this works about 33 per cent of the time ( but i aim pretty high at this point )

Ive met and shot with a ton of Good Models on MM over the Years , as well as a handful.in Local FB Groups and on IG ( I am still trying to make that work better for me but i realize that part of my problem is that i am too lazy to grow my followers and I am about 3 years behind in posting photos )

Established Pro Models on Social Media  get hundreds of requests from Photographers wanting to shoot with them ( from legit Photographers to complete scammers )  - I know this having talked with some such Models

I dont think there is much "validation " for Models ( or Photographers ) in having someone average ( like myself ) wanting to work with them . The real validation comes from the Shoot , the resulting Photos and the Possible Opportunities that develop from the aforementioned