Use react-select with Formik

example.tsx

const options = [
  { value: 'foo', label: 'Foo' },
  { value: 'bar', label: 'Bar' },
]

return <Field name={'example'} component={SelectField} options={options} />

SelectField.tsx

import { FieldProps } from 'formik'
import React from 'react'
import Select, { Option, ReactSelectProps } from 'react-select'

export const SelectField: React.SFC<ReactSelectProps & FieldProps> = ({
  options,
  field,
  form,
}) => (
  <Select
    options={options}
    name={field.name}
    value={options ? options.find(option => option.value === field.value) : ''}
    onChange={(option: Option) => form.setFieldValue(field.name, option.value)}
    onBlur={field.onBlur}
  />
)

I just did this...
onValueChange={(val) => formik.setFieldValue('timezone', val)}