Creating an auto complete search using angularfire2 and firestore?

It is pretty much the same with Firestore.

Here the working and tested solution i just wrote :

search.ts

import { Component } from '@angular/core';
import { AngularFirestore } from 'angularfire2/firestore';

@Component({
  selector: 'search',
  templateUrl: 'search.html'
})
export class SearchComponent {

  searchValue: string = "";
  results: any;

  constructor(public afs: AngularFirestore) {
  }

  search() {
    let self = this;
    self.results = self.afs.collection(`users`, ref => ref
      .orderBy("username")
      .startAt(self.searchValue.toLowerCase())
      .endAt(self.searchValue.toLowerCase()+"\uf8ff")
      .limit(10))
      .valueChanges();
  }

}

search.html

<div>
  <input type="text" (keyup)="search()" [(ngModel)]="searchValue">
  <div class="search-results">
    <div class="search-result" *ngFor="let result of results | async">
      {{ result.username }}
    </div>
  </div>
</div>

If you need a more complex search, you could use Algolia :

To enable full text search of your Cloud Firestore data, use a third-party search service like Algolia. Consider a note-taking app where each note is a document:

You'll find more information on the official firestore documentation