Please tell us here how we can help, MFFJM2. And how we mess up. Be brutal- we are behind screens lol.
Thanks Sir/Ma'am and thanks for what ya'll do.
IMHO this is what you, what we all can do.
You can keep passing pictures on flyers around the area where she was last seen, and then in ever widening circles. Myrtle Beach as a starting point, and then out to gas stations frequented by truckers. You can try to get the family of the missing person to go on TV, especially nationally sydicated shows like "America's Most Wanted" with pictures of the missing person. The more people that see the pictures the more likely someone will remember her, and that will help the police find her.
When parents go on TV they should also show pictures of the missing or abducted person from when they were a baby or infant. Never appear angry or as someone who desires revenge.
In the best of all situations the person who is travelling with her, possibly posing as a parent, will decide there's too much heat and simply drop her at a bus station.
That Abigail was permitted to write a letter to her mother tells us that although possibly manipulated or coerced she was still alive and likely uninjured.
Leave the police and the FBI to do their work without constantly asking for updates, and then complaining when they aren't forthcoming.
Hold candlelight vigils for the safe return of the victim, and get the local press involved. Hold birthday parties for the victim, and get the press involved. Use every opportunity to get pictures of the missing person to the press. Somewhere there's a person, not involved in the abduction, who knows what's going on, and that is the person you're trying to reach. This case is not a serial killer case, but that doesn't mean it couldn't turn deadly.
"What kinds of things should we focus on when keeping an eye out for her?"
People change over time, and if she is travelling with someone they may be insisting she disguise herself (wigs, hair color, sunglasses, clothes, etc).
"I wonder how someone might recognize her, especially if she's changed her appearance (hair cut, hair color, different clothes)?"
The jawline, height, weight, eye color, and any scars or distinguishing marks are good methods for recognizing people, even in disguise. Piercings, tattoos, and birthmarks are especially helpful. If you think someone is using a disguise, and they're a minor, ask them if they're okay, and trust your instincts. Remember that young girls can be dressed as boys.
If it doesn't seem right, take down everything: time of day; location; direction they came and went; if they have a vehicle, and all the particulars about that vehicle; clothing; and what if anything they were doing that you observed. Report that information to the police and the FBI. Elizabeth Smart could have been rescued much earlier if people simply followed that advice.
'Mannerisms"
Unless you're a close friend or a family member these mannerisms will not be known to you.
"Thing is, if any of my children were missing they could change a lot but I'd still recognize them by their voice, or their mannerisms or their eye shape, etc. It's harder when it's someone you've never met and you only see two dimensional photos. I'm sure that to her family AH looks the same in all the pics we've seen, but in some of the pics she looks like another person. I wonder and worry that people may be passing her on the street and not even recognize her because they don't know her. So what should people focus on when looking for her?"
This is why as many pictures of her as possible in differing clothes and different situations should be used, rather than simply the latest photo.
"And I can understand why it's not helpful to release the contents of the letter, but why not the postmark? At least to know if she travelled south or north or east or west? I'm sure that wherever that postmark was from is probably not where she is now, but it would be helpful to know what direction she travelled in."
Two things can happen if the person travelling with AH gets frightened, he can drop her or he can hurt her. The main desire of law enforcement is to get the former without the perpetrator considering the latter. We want the pressure of travelling with this child to become too great to continue as they have, but not so great that he thinks murder is a solution. This is a tightrope, and you should believe that those who have the experience are doing what's best.
"And is there a chance that an amber alert could still be issued if someone were to come forward with a description of a car or a person they saw with her that day on her walk home?"
An Amber Alert is always possible if the police have credible and timely evidence of a location, vehicle, and direction, but the witness report needs to be of them as they are now, not as they were two or three months ago.
"For example, if someone had been up there leaf-peeping and didn't know this had happened and turned on the news tomorrow and heard about for the first time and realized they had seen something."
All witness statements are valuable, and need to be processed according to the rules of evidence. Anyone who has any information about Abigail Hernandez should contact their local police at once, even if it was just a passing contact.